Origins Seminar Series Event Archive

Origins Seminar series

The Origins Seminar series aims to bring together ISM, star and planet formation people, exoplanets experts, planetary scientists and astrobiologists including topics from molecular clouds through star and planet formation to exoplanets detection and characterization and astrobiology.

The seminar series is organized by Serena Kim (SO), Kamber Schwarz (LPL) and Sebastiaan Haffert (SO) from Steward Observatory/Dept. of Astronomy and Dept. of Planetary Sciences (LPL) at the University of Arizona. The Origins Seminar series is partly supported by the Earths in Other Solar Systems NExSS team.

During regular semesters, talks are generally from 12pm – 1:00pm (MST) on Mondays. 12PM Arizona Time (MST) = 12pm PDT = 3pm EDT = 7pm UTC. If you want to receive weekly updates and advertisements for talks, please subscribe to the mailing list.  If you are interested in presenting your work during one of the open slots (see below), feel free to contact the organizers: serena00 at email.arizona.edu,shaffert at email.arizona.edu,huangcl at arizona.edu. 

During the Fall semester (just like Spring and Summer) 2020, the Origins seminar will meet via Zoom due to the Covid-19 Pandemic. The Zoom information is sent via email, and the Origins seminar talks are recorded.

Visit the Origins Seminars page to view upcoming talks!

Spring 2025

Short Talks

Feb 03, 2025   |   12 pm noon (MST)   |   Hybrid (Steward 305 & Zoom)
Schuyler Wolf, University of Arizona (Steward)
Dingshan Deng, University of Arizona (LPL)
Griselda Arroyo-Chavez, University of Arizona (Steward)
Chengyan Xie, University of Arizona (LPL)
ABSTRACT

Short talks from Origins members on their recent work and events of interest to the Origins community.

WATCH VIDEO

New Stellar Dynamical Masses in Upper Scorpius:
A Critical Test of PMS Evolutionary Models

February 17, 2025   |   12 pm noon (MST)   |   Hybrid (Steward N305 & Zoom)
Allison Towner, University of arizona (Steward)
ABSTRACT

In this talk, I will discuss recent work comparing dynamical masses and ages for 23 low-mass PMS stars in Upper Scorpius to those returned by five different sets of stellar evolutionary models. We use the new dynamical masses to evaluate the accuracy of the isochronal results, including whether any of the models are more or less accurate in particular mass ranges. We find that most isochronal methods consistently underestimate stellar mass and age. The exceptions are the magnetic models of Feiden (2016), which are generally in good agreement with the dynamical results already, and the PARSEC v1.2S models, which tend to return larger-than-dynamical masses for the lowest-mass stars (M ~ 0.1 Msun) and smaller-than-dynamical masses for our higher-mass stars (M ~ 1 Msun). We derive disk dust masses for these sources, and find that the use of dynamical rather than isochronal masses does not significantly impact the slope of the log(M_disk) vs log(M_star) relation. Finally, we examine the MCMC fitting procedure itself, and determine that traditional methods of estimating parameter uncertainty (e.g. standard deviation of the walkers) are likely underestimating parameter uncertainties by factors of 2 to 3.

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GUSTO and the Future of Far-Infrared Astronomy

February 24, 2025   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
Chris Walker, University of Arizona (Steward)
ABSTRACT
The Galactic/Extragalactic Spectroscopic Terahertz Observatory (GUSTO) is a NASA 0.9m balloon-borne observatory launched on December 31st, 2023 near McMurdo Station, Antarctica. Over its record-breaking, 57+ day mission, GUSTO carried out large-area surveys in two key fine structure lines in [NII] and [CII] with km/s velocity resolution. GUSTO‘s stratospheric mission (altitude: 30-35 km) allowed us to carry out these terahertz (THz) observations essentially unhindered by the Earth’s atmosphere. These THz data will allow GUSTO to address key questions about the life cycle of the ISM, including 1) the structure of warm neutral regions participating in and affected by star formation (with [CII]), 2) gas ionized by massive stars (with [NII]), and, when combined with ancillary observations, 3) the neutral dense photon-dominated regions (PDR) powered by massive young stars. Three surveys were conducted: a Galactic plane survey covering 62 sq. deg. within |l|< 3 deg, a Large Magellanic Cloud survey covering 2.3 sq. deg., and targeted deep surveys. The Galactic plane survey provides 3-dimensional, high spectral resolution images from which the complexities of the ISM can be disentangled, probing all phases of its life cycle. The observations of the LMC allow investigation of star formation in a low-metallicity environment, and provide a template for the ISM and star formation in distant galaxies. The targeted deep surveys allow detection of more extended neutral and ionized gas and the relationships of HII regions and PDRs. The entire GUSTO database will soon be made available to the community for analysis and study through University of Arizona and IPAC data archives. During the first part of the talk, I will discuss the GUSTO design, implementation, flight, and early science results. I will then discuss the next 10 years and the possibilities for follow-on far-infrared observatories in the remote reaches of Antarctica, the stratosphere, and beyond.
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The Giant Planet Formation Time Window: An Observational Perspective

March 03, 2025   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Cheng-Han Hsieh, University of Texas – Austin
ABSTRACT
One of the main unsolved problems in planet formation is pinpointing when the process starts. A crucial aspect of this quest involves identifying substructures within circumstellar disks, which could serve as early indicators of planet formation. The high angular resolution observations by ALMA have been a game-changer in the field and revealed for the first time substructures in disks with unprecedented details. However, these surveys focused on more evolved Class II disks or the brightest, largest disks. We present the CAMPOS Legacy survey, an ALMA survey of embedded Class0/I and Flat protostellar disks in the star-forming clouds of Chamaeleon, Ophiuchus, Aquila, Corona Australis, and Serpens. We probed over 90 disks down to 15 au resolution and conducted the first statistical search for disk substructures around Class 0/I protostars. Our findings reveal compelling evidence suggesting a lack of substructures in young Class 0 and early Class I disks. Intriguingly, disk substructures begin to emerge only in sources with a bolometric temperature exceeding 110 K, indicating the rapid evolution of disk substructures during the Class I phase. Our CAMPOS survey has for the first time discovered how early disk substructures form and, as a corollary, when giant planet formation begins.

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The Search for Galactic Relics: Characterizing the Oldest, Metal-poor Brown Dwarfs and M-dwarfs in JWST Deep Fields

March 17, 2025   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Jorge Sanchez, Arizona State University (SESE)
ABSTRACT
The North Ecliptic Pole Time-Domain Field (NEP-TDF) component of the deep extragalactic survey PEARLS (Prime Extragalactic Areas for Reionization and Lensing Science), covers approximately 55 square arcminutes with 8 NIRCAM filters to a depth of about 28.5 (AB). Although designed as an extragalactic survey, the field is exceptionally sensitive to search for brown dwarfs in the Galactic thick disk or halo. The broad wavelength coverage from 0.9 microns to 4.4 microns can be leveraged to discriminate cool brown dwarfs from extragalactic sources. Given the much older age of the thick disk/halo population relative to the solar neighborhood, brown dwarfs at these large scale heights above the disk are likely to be lower metallicity compared to nearby substellar objects, making these distant brown dwarfs valuable benchmarks for testing atmospheric models. We report the discovery of a population of brown dwarf and M-dwarf candidates spanning from early-M to late-T dwarfs. Substellar candidates are identified by comparing the JWST photometry with synthetic photometry constructed from current models of the Sonora Elf Owl grid. We further differentiate the candidates from high redshift galaxies by comparing the NIRCam data with empirical templates of Active Galactic Nuclei (AGN). We present distance, effective temperature ,metallicity and CtoO estimates for the candidates M, L and T dwarfs in the NEP-TDF field. The physical properties of the NEP sample are compared with field brown dwarfs as well as substellar objects identified in other extragalactic fields with JWST. The characterization of these objects with follow-up spectroscopy is critical for understanding the distribution of brown dwarfs on the kilo-parsec scale, and investigating the origins of some of the oldest, metal-poor objects in the galaxy.

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CO line emission supports large protoplanetary disk masses without significant CO depletion

March 24, 2025   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
 Dingshan Deng, University of Arizona (LPL)
ABSTRACT
CO is one of the most abundant molecules in protoplanetary disks, and emission from CO isotopologues has been detected in many of them. However, several past works contend that reproducing the observed low C18O luminosities might require a significant reduction in the gas-to-dust mass ratio (down to ~ 1) or CO depletion (up to ~ 100), suggesting that CO is not a good tracer of the bulk disk mass. Here, we present a model that uniquely considers a density and temperature structure consistent with the thermal pressure gradient in the disk and CO conversion to CO2 on grains. We apply the model to the large disks in the Lupus star-forming region in the literature and smaller disks from the new observations from the ALMA large program AGE-PRO. We infer these disks have larger masses than the values in the literature, along with interstellar-medium-like gas-to-dust mass ratio without significant CO depletion. We also show the published open-source Python-Fortran code DiskMINT (Disk Model for INdividual Targets) and how it can be used to weigh the masses of other disks to weigh their masses using emissions from CO isotopologues.

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Planet-Forming and Photoevaporating Disks in the Orion Nebula Cluster: The View from ALMA and JWST

March 31, 2025 | 12 pm noon (MST) | Hybrid (Steward N305 & Zoom)
 Nick Ballering, University of Virginia
ABSTRACT
The Orion Nebula Cluster (ONC) offers the clearest view of protoplanetary disks in a rich cluster, the typical environment for star and planet-formation in the Galaxy. I will present results from high-resolution ALMA observations of over 200 disks in the ONC that reveal their dust masses and sizes, key properties in determining what types of planets can form. I will also highlight images of proplyds—disks in the process of being photoevaporated by the cluster’s harsh radiation field—where ALMA traces free-free emission and radio recombination lines from outflowing ionized gas. I will then turn to the infrared and share recent JWST NIRSpec observations of warm atomic and molecular gas from three ONC proplyds. Finally, I will show how JWST NIRCam observations can reveal the presence of water ice in an edge-on disk seen in silhouette in front of the Orion Nebula.
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Numerical simulations of protostellar disk formation with non-ideal magnetohydrodynamics and protostellar feedback

April 07, 2025 | 12 pm noon (MST) | Hybrid (Kuiper 309 & Zoom)
 Nina Filippova, University of Texas – Austin
ABSTRACT
Protostellar disks are expected to form early during the star formation process due to conservation of angular momentum throughout the collapse. While recent surveys have resolved disks around hundreds of nearby protostars, numerical simulations assuming ideal magnetohydrodynamics (MHD) have historically struggled to achieve disk formation due to efficient angular momentum removal by magnetic torques – the “magnetic braking catastrophe.” Non-ideal MHD effects, which become relevant at the low ionization fractions typical of molecular clouds, have been shown to reduce the effectiveness of magnetic braking. However, many numerical studies of disk formation also adopt highly-idealized initial conditions of isolated spherical cores collapsing to form individual protostars. This setup may exaggerate the influence of magnetic braking. Furthermore, most stars are born as members of bound systems, and dynamical interactions between stellar neighbors likely affect subsequent disk evolution. A comprehensive study of disk formation and evolution must therefore incorporate both external dynamics as well as increasingly sophisticated physics. In this talk, I will present the results from a suite of numerical calculations following the collapse of turbulent, magnetized 50 solar-mass cores down to the formation of stellar clusters and disks using the 3D radiation+gravity MHD code GIZMO, with additional modules for protostellar feedback developed within the STARFORGE numerical framework. These simulations aim to investigate the effects of including non-ideal MHD and realistic protostellar feedback on disk formation and evolution within the context of multiple star formation.
WATCH VIDEO

Revisiting the Core Accretion Paradigm for Giant Planet Formation:
Analytic Framework for the Late Infall Stage and the Distribution of Planetary Masses

April 21, 2025 | 12 pm noon (MST) | Hybrid (Kuiper 309 & Zoom)
 Fred Adams, University of Michigan

This presentation will be held jointly with the Theoretical Astrophysics Program (TAP)

ABSTRACT
This talk presents an analytic description for the late stages of giant planet formation, when planets gather the majority of their mass. The resulting solutions show how the protoplanet properties (envelope density distribution, velocity field, column density, disk surface density, system luminosity, and emergent spectral energy distributions) vary with the input parameters of the problem (instantaneous mass, orbital location, accretion rate, and planetary magnetic field strength). We then construct a framework for calculating the distribution of planet masses resulting from this paradigm. In this scenario, the disk lifetime determines the end of mass accretion onto the planet. The mass accretion rate depends on the size of the Hill sphere, the fraction of the disk accretion flow that enters the sphere of influence, and the efficiency with which the planet captures the incoming material. The resulting model produces a planetary mass function with a nearly power-law form, roughly consistent with current observational estimates.
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From Pebbles to Planets: Dust Dynamics in Planet Formation Processes

April 28, 2025 | 12 pm noon (MST) | Hybrid (Steward N305 & Zoom)
 Ziyan Xu, University of Copenhagen
ABSTRACT

Dust grains are the building blocks of planets. Recent millimeter-wavelength observations have revolutionized our understanding of protoplanetary disks, revealing that mm-cm sized dust grains, or pebbles, are abundant in disks, and are commonly seen in ring-like structures. These pebbles play a crucial role in planet formation, for both planetesimal formation via streaming instability and embryo growth through pebble accretion. Both processes are governed by dust dynamics, which are highly sensitive to the surrounding gas conditions including turbulence and thermodynamics. In this talk, I will present (magneto-)hydrodynamic simulations of dust dynamics in both planetesimal formation and pebble accretion under realistic gas environments, with implications for disk observations and cosmochemistry. I will first show that turbulent dust-trapping rings are ideal sites for planetesimal formation, and that gas-dust interactions can shape ring structures. I will also discuss how dust evolution may potentially enhance this effect. Next, I will demonstrate that in convective gas envelopes around growing protoplanets, pebble accretion remains generally efficient, but volatiles may be rapidly lost, implying that the Earth could have formed through a hybrid accretion pathway. Finally, I will introduce ongoing efforts to simulate local hydrodynamics and dust dynamics during protostellar collapse.

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Measuring protoplanetary gas-disk properties: early DECO results

April 29, 2025 (Tuesday) | 12 pm noon (MST) | Hybrid (Location TBD & Zoom)
Luigi Zallio, University of Milan
ABSTRACT

Talk given April 29, 2025. Observations of planet formation are undergoing rapid development, mostly thanks to the transformational capabilities of the ALMA observatory. ALMA relies on molecular spectroscopy to determine the spatially resolved physical conditions in the gas reservoirs of disks. To explore this new frontier, analysis tools capable of retrieving all the information hidden in the data are essential. Usually, this kind of analysis relies on analysis of images. In interferometry these are however highly processed data products, and this introduces systematic biases which are difficult to quantify. I will present a different strategy which instead analyses the data directly in the visibilities, the native quantity measured by the interferometer. The analysis, implemented in the code CSALT, is based on a parametric model of the disk structure and emission; this approach allows a robust statistical inference of the model parameters and allows to infer a size also for disks that in the image plane are only marginally resolved. Measuring gas-disk sizes is of fundamental importance to understand how proto-planetary disks form and evolve. The viscous evolutionary paradigm predict that disks enlarge as a function of time, while the MHD wind-driven one states that they shrink due to angular momentum loss. Until now, it was impossible to test these predictions on a statistically significant scale, but with the advent of the DECO Large Program (P.I. Ilse Cleeves), which observed 80 “common” discs in 4 regions with different ages, we now have enough data to constrain this key prediction. In this talk, I will present preliminary results obtained for a subset of proto-planetary disks with new analysis techniques. I will show the models obtained for disks in the three isotopologues 12CO, 13CO, C18O coming from the Large Program DECO, and I will outline the developments that I obtained with respect to other analysis approaches. This new method leads to an unprecedented possibility of parametric-modelling inference, opening the possibility to rely on robust interpretation of physical properties also for barely resolved disks.

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Mining for GEMS – Characterizing big planets around small stars

May 05, 2025 | 12 pm noon (MST) | Hybrid (Kuiper 309 & Zoom)
 Caleb Canas, NASA Goddard Space Flight Center
 ABSTRACT
Talk given May 5, 2025. Short period (P less than 10 days), giant exoplanets (Rp larger than 8 Earth radii) around M-dwarf stars (GEMS) represent a growing exoplanet population that is often difficult to reconcile with existing theories of planetary formation. I will discuss the efforts to detect and characterize these planets using a combination of space- and ground-based facilities. These efforts include the “Searching for GEMS” photometric and RV ground-based survey and a companion survey to measure stellar obliquity. I will also discuss efforts to characterize the atmospheres of these planets as a means of investigating formation pathways with a JWST survey: “Red Dwarfs and the Seven Giants” (GO 3171), which has observed 7 GEMS, and has a goal of deriving the atmospheric and bulk metallicities for these planets. I will present the results for TOI-5205 b, a Jupiter analogue orbiting a mid M-dwarf and the first of these GEMS observed with transmission spectroscopy.

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On angular momentum from molecular cloud to core scales

May 12, 2025| 12 PM Noon (MST) | Hybrid (Steward N305 & Zoom)
Griselda Arroyo-Chavez, University of Arizona (Steward)
 ABSTRACT
The Angular Momentum Problem (AMP), viewed as the apparent loss of specific angular momentum (j) as a function of radius (R) for density structures at molecular cloud to core scales, has been a topic of interest in the last decades for which different solutions have been proposed in the literature. These solutions are based on different physical mechanisms involving turbulence, gravity, or magnetic field. In the first part of this work, we study the j-R relation and its evolution in a sample of clouds, clumps, and cores defined in SPH-type simulations of the formation, collapse, and fragmentation of giant molecular clouds in the warm neutral medium. For the second part, we focus on studying the nature of the angular momentum transfer mechanism by measuring the active torques in the previously defined numerical clumps. We find that the torques that dominate in magnitude over the magnetic, gravitational, and pressure-gradient torques are the torques we call hydrodynamic torques, which include the effect of turbulent viscosity.

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Fall 2024

OSIRIS-REx: Insights from the Asteroid Bennu and Initial Analysis of the Returned Samples

August 26, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
 Dante Lauretta, University of Arizona (LPL)
ABSTRACT

The OSIRIS-REx mission has been a pivotal step in our understanding of near-Earth asteroids and the early solar system. This presentation will delve into the mission’s journey to Bennu, the challenges faced in collecting samples, and the wealth of data returned. It will highlight key findings from the initial analysis of the samples, offering insights into Bennu’s composition and its implications for theories on the formation of the solar system and the origins of life. 

OSIRIS-REx Project: https://osirisrex.arizona.edu/

WATCH VIDEO

Effect of stellar flares on atmospheric escape of terrestrial planets

September 09, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
 Laura Amaral, Arizona State University
ABSTRACT

The habitability of planets around M dwarfs (=<0.6 solar masses) can be affected by the X-rays + extreme UV (XUV) emission of these stars, with flares occasionally increasing the XUV flux by more than two orders of magnitude above quiescent levels. This wavelength range can warm and ionize terrestrial planets’ upper atmospheres, which expands the planetary radius and promotes atmospheric loss. In this talk, I will show how the contribution of the XUV flux due to stellar flares affects the atmospheric escape of Earth-like planets orbiting M dwarfs through numerical simulations. The simulations considered the first Gyr of planets with initial surface water abundances between 1 and 10 terrestrial oceans (TO), a small primordial hydrogen envelope (~0.001 earth masses), and host-star masses between 0.2 and 0.6 solar masses. The results show that flares can remove up to two TO more than non-flaring stars, which sometimes translates to a doubling of the total water loss. In some cases, flaring can increase atmospheric oxygen partial pressures by hundreds of bars.

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Three-temperature radiation hydrodynamics with PLUTO: A powerful tool to investigate protoplanetary disks

September 10 (Tuesday), 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Dhruv Muley, Max-Planck-Institut für Astronomie (MPIA)
ABSTRACT
High-resolution observations of protoplanetary disks at a range of wavelengths have uncovered a wealth of large-scale substructures—including gaps, rings, and spirals—often attributed to the gravitational influence of nascent planets. This process has long been studied using numerical hydrodynamics simulations, with recent works demonstrating that thermodynamics have a significant influence on substructure morphology. To more realistically handle thermal physics, we have developed a “three-temperature” (3T; gas, dust, radiation) radiation-hydrodynamics scheme which includes collisional thermal relaxation between dust (which supplies most of the opacity) and gas (which holds most of the heat capacity). In the upper atmosphere, the collisional thermal relaxation time reaches order-unity of the dynamical time, allowing planet-driven perturbations to decouple the dust and gas temperatures. We apply 3T to open questions inspired by observed disk substructures such as the gas-kinematic and temperature spirals in TW Hya and the large-scale, double-armed spirals in SAO 206462/HD 135344B.
WATCH VIDEO

The Role of Magnetic Fields in Star Formation: First Complete 3D Vector Observations

September 16, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 Mehrnoosh Tahani, Stanford University
ABSTRACT
Polarimetry observations over the past decade have highlighted the critical roles that magnetic fields play in the formation of clouds and stars. Despite their importance, observing these magnetic fields, particularly in 3D, remains significantly challenging. In this talk, I will briefly discuss how we overcame these challenges in determining the 3D magnetic field vectors associated with giant molecular clouds. Our findings have enabled us to propose step-by-step scenarios explaining the formation of these clouds, revealing previously undiscovered interstellar structures. These 3D studies provide novel constraints on theories for the formation and evolution of star-forming clouds, advancing our understanding of the role of magnetic fields in star formation.

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Exoplanetary Epics: Environmental Storytelling Across Planetary Systems

September 23, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
 Quadry Chance, University of Florida
ABSTRACT
With thousands of confirmed exoplanets, we now have access to clues about planets and planet formation embedded in planet hosts’ past and present environments. This has already yielded many successful models of how we expect planetary systems to behave. Examining where some of these models start to break down and determining if we need new components has been the main focus of my PhD work. Paired pipeline can be found here.

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A framework for modeling the evolution of young stellar objects

September 30, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 Theo Richardson, University of Florida
ABSTRACT
Measuring the properties of young stellar objects (YSOs) is a key part of research into the pre-main-sequence evolution of stars. Due to the complex geometry of YSOs, measurement generally takes the form of comparing observed radiation to existing template populations of YSO SEDs modeled using radiative transfer. However, owing to uncertainty on the precise mechanics of star formation, the properties of YSOs inferred from these models often depend on the accretion history assumed in the construction of the templates. I have developed a framework for predicting the properties and SED of a YSO that is agnostic to the underlying theory, enabling comparison between theories. I present results generated using this framework, discuss their ramifications for observational studies of YSOs, and preview future development.

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Characterizing disks and planets from the ground and space

October 4 (Friday), 2024   |   10 am (MST)   |   Hybrid (Steward 450 & Zoom)
Matthias Samland, Max-Planck-Institut für Astronomie (MPIA)
ABSTRACT
In this talk I will provide a broad overview of exciting results we have recently obtained VLT/SPHERE and JWST in the area of protoplanets and debris disks. I will give a broad overview of methods and tools I have developed for direct imaging of planets and disks over the years with application to my “B-Stars in Orion: Imaging Newly-formed Companions” (BOINC) survey. On the JWST side I will discuss highlights from the MIRI mid-INfrared Disk Survey (MINDS, PI: Henning) with a focus on PDS 70 and the most intriguing results on debris disks, such as how MIRI integral field spectrograph can be used to image debris disks across the mid-IR, and the exciting discovery of evaporating asteroids around a nearby star.

The JWST-MIRI View of a Gas-Rich Disk with a Large Dust Cavity

October 7, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
 Kamber Schwarz, Max-Planck-Institut für Astronomie (MPIA)
ABSTRACT
SY Cha is a T Tauri star surrounded by a protoplanetary disk with a large cavity seen in the millimeter continuum but with the spectral energy distribution of a full disk. I will present the first results from JWST-MIRI Medium Resolution Spectrometer (MRS) observations taken as part of the MIRI mid-INfrared Disk Survey (MINDS) GTO Program. The derived molecular column densities reveal the inner disk of SY Cha to be rich in both oxygen and carbon bearing molecules. Additionally, we detect spatially extended H2 emission seen in five transitions as well as a jet traced by [Ne II]. Analysis of the extended H2 points to a molecular disk wind with a low mass loss rate. All of these results are in contrast to PDS 70, another protoplanetary disk with a large cavity observed with JWST, which displays much weaker line emission and no strong outflow. I will discuss how these results inform our understanding of gap opening mechanisms and mass loss in protoplanetary disks.
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Dynamics of Star Formation on Different Scales: Protostellar Envelopes, Binaries/Multiples, Disks, and Jets

October 14, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Yisheng Tu, University of Virginia
ABSTRACT
Star and planet formation is a complex process involving processes across all scales. In this talk I will present three sets of simulations, each focusing on a different scale, to illustrate the key processes involved in each scale. At the largest, molecular cloud core scale, the “gravo-magneto-sheetlet”, an intrinsic 3D structure due to the interaction between turbulence, magnetic field, and gravity, dominates mass and magnetic flux transport in the protostellar envelope; in the disk, the magnetic braking dominates angular momentum transport over gravitational torque, with the level of dominance determined by the strength of the non-ideal MHD effect. In more massive and faster rotating molecular cloud cores, the gravo-magneto-sheetlets develop into a highly dynamic structure that we termed “Dense ROtation-Dominated (DROD) structure.” Provided the DROD is sufficiently demagnetized, it would fragment into multiple stellar objects through the “DROD-fragmentation mechanism,” which can form in-situ 100 au-scale multiple systems with misaligned disks. At the disk scale, we investigated grain growth in protostellar environments, motivated by the observations of large (mm/cm-sized) dust grains in protostellar disks. We show that grain growth is slow in laminar protostellar disks, requiring at least a factor-of-4 increase in grain growth rate to produce large grains in early protostellar environments. The result is supported by an analytic solution of the Smoluchowski coagulation equation, highlighting the role of grain concentration and grain-grain collision speed in determining the growth rate. At the inner disk scale, we demonstrated that the jet is powered by the so-called “avalanche accretion streams,” a magnetically braked raised disk atmosphere that exhibits avalanche-like infall due to a positive feedback loop between infall, magnetic braking, and angular momentum removal. The avalanche accretion streams also facilitate magnetic reconnection, preventing excessive magnetic flux accumulation close to the protostar, and may contribute to heating and transporting Calcium-Aluminum-Inclusion (CAI) chondrules in the early Solar system.
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The relation between magnetic field strength and gas density: A multiscale analysis

October 21, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
 David Whitworth, Universidad Nacional Autónoma de México (UNAM)
ABSTRACT
Magnetic Fields are ubiquitous in the universe, from planetary magnetospheres to the primordial background field. They play key roles in various aspects ISM physics within galaxies, from their growth and pressure support across the multiphase medium to the suppression of star formation in regions of high field strengths. Since the seminal work of Crutcher at al 2010 there has been a well known relationship between magnetic field strength and gas number density derived from 137 Zeeman observations. Over the last 14 years we have seen a wealth of new observational data from DCF measurements and a rapidly growing field of new MHD numerical simulations. By looking at theory, observations and numerical models we are able to look at a much larger density range, from the most diffuse ISM to stellar cores and re-examine this relationship. I will show through a systematic and statistical analysis of the observational data how we can build upon the original relationship, focusing on the diffuse medium where originally there was no correlation between gas density and field strength. We find a new, generalised, time-dependent observational relationship with exponents in both the diffuse and dense gas. Finally, by looking at numerical simulations with a similar statistical technique we are able to determine astrophysical processes that drive the relationship across scales. Attendees may be interested in reading this preprint before the talk: https://arxiv.org/pdf/2407.18293

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Explaining the Diversity of Extrasolar Worlds

October 28, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Genaro Suarez, American Museum of Natural History 
ABSTRACT

The observation and modeling of substellar objects such as brown dwarfs and exoplanets allow us to understand the physics and chemistry that govern their atmospheres, which is essential to explain their diversity. In this talk, I will show progress we have in explaining the appearance of extrasolar worlds, from the hottest (~2300 K) to the coldest (~400 K) ones. Particularly, I will present results on the formation, composition, evolution, and distribution of dust clouds that shape the emergent spectra of the warmest brown dwarfs and exoplanets using Spitzer and JWST mid-infrared spectra. In addition, I will show JWST results that are guiding us in understanding the physical and chemical processes that domain the coldest extrasolar atmospheres.

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Kaleidoscope of irradiated disks: VLT/MUSE observations of proplyds

November 4, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 312 & Zoom)
Mari-Liis Aru, European Southern Observatory (ESO)
 ABSTRACT
The evolutionary pathways of protoplanetary disks, the birthplaces of planets, differ depending on the surrounding environment. In massive star clusters, UV radiation affects disks via external photoevaporative winds, depleting the disks outside-in and severely shortening their lifetimes. Known as proplyds, such irradiated disks are typically surrounded by a teardrop-shaped cloud of ionized gas and observed in forbidden emission lines. While external photoevaporation of disks is unique to clusters such as the Orion Nebula Cluster (ONC), internal photoevaporative winds may be present in both high UV environments, and low-mass star forming regions with weak external UV fields. In the latter case, the winds arise due to radiation from the central star and can also be studied via forbidden line emission. It is therefore crucial to determine how to disentangle external winds from internal ones. I will present the results based on the visually striking VLT/MUSE IFU data of a dozen proplyds in the ONC. This sample allows us to study the morphology of proplyds in a wealth of emission lines and determine their physical parameters. Among the results, I will present a proxy for unambiguously identifying externally driven winds with a forbidden line of neutral atomic carbon.

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Organosulfur Chemistry in the Birthplaces of Stars and Planets

November 12 (Tuesday), 2024   |   12 pm noon (MST)   |   Hybrid (Steward N305 & Zoom)
Suchitra Narayanan, Harvard University
 ABSTRACT
Of the elements critical for life, sulfur is poorly understood due to its 1–2 orders of magnitude depletion in the gas phase of star-forming regions (also known as the “missing sulfur problem”). To reconcile this, sulfur is believed to be locked up in icy grains; however, the sum of the solid sulfur inventory in ices accounts for only ≤ 4% of the cosmic sulfur abundance. The most updated astrochemical gas-grain reaction network predicts that this observed sulfur depletion could be explained if the majority of the sulfur exists in the form of solid organosulfur species. However, due to the limited number of solid-state sulfur experiments, this model, like many others, heavily depends on the theoretical assumption that sulfur and oxygen chemistry proceed comparably. My PhD dissertation fills this gap in literature by characterizing the simplest S-bearing complex organic molecule, methyl mercaptan (CH₃SH), with respect to its well-studied and relatively abundant O-bearing counterpart, methanol (CH₃OH). I present new laboratory experiments on CH₃SH’s thermal desorption kinetics, entrapment behavior, and formation/destruction pathways, while contextualizing all results with analogous CH₃OH experiments. This allows us to probe for the first time in the laboratory how, when, and why does S vs. O chemistry proceed (dis)similarly. In most cases, I find that under identical experimental conditions, CH₃SH behaves differently from CH₃OH, and these discrepancies cannot be fully explained with current computational chemistry capabilities. In particular, we find that the physical and chemical properties of a molecule (e.g., size, ability to form allotropes, bonding potential) significantly affects its behavior and stability in astrophysically relevant conditions. This is the first time that such a size effect has been shown to impact solid-state chemistry significantly. By studying how two theoretically similar elements are empirically different, my work serves as a foundational guide for further investigations into more complex molecules, enabling us to better predict their behavior based on whether they exhibit characteristics similar to sulfur or oxygen. I also use key findings from the laboratory to inform my complementary theoretical studies and observational programs with the Atacama Large Millimeter/submillimeter Array and the  Submillimeter Array, where I probe sulfur chemistry in the earliest stages of star and planet formation. Overall, these results both emphasize the necessity of dedicated sulfur experiments and highlight the value of comparative chemistry for rationalizing observations and refining the theoretical understanding of sulfur (astro)chemistry.

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The exotic gas composition around TRAPPIST-1 progenitors unveiled by JWST

November 14 (Thursday), 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
Aditya Arabhavi, Kapteyn Astronomical Institute

ABSTRACT
Terrestrial planets such as Earth are some of the most common type of planets in the universe, and very low-mass stars (<0.3 solar mass) are the most common type of stars. Young stars host disks of gas and dust which eventually form these planets. The inner regions of these disks can be probed with infrared wavelengths. While the faint nature of such sources limited the detailed characterization with Spitzer Space Telescope, the high sensitivity and spectral resolving power of JWST/MIRI has unvieled unprecedented details of the gas compositions of such disks. In this talk, I will present the first results concerning disks around such very low-mass stars from the MIRI midINfrared Disk Survey (MINDS) JWST GTO program. These disks are found to be dominant in carbon-bearing molecules from single carbon atom up to six carbon atoms, contrasting with the typically oxygen-rich species found in disks around solar mass stars. The chemical inventory and the line fluxes indicate high C/O ratio in these disks and present interesting trends.

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Modeling Earthshine Observations for Future Exoplanet Reflected Light Missions

November 18, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
Giulia Roccetti, European Southern Observatory (ESO)

 

 ABSTRACT
The next generation of ground- and space-based telescopes, including ANDES and PCS at the ELT and the mission concept Habitable World Observatory (HWO), will make it possible to study exoplanets in reflected light, extending this capability to rocky planets. Earthshine, the sunlight reflected by Earth onto the Moon, provides an opportunity to capture spatially unresolved properties of Earth as seen in reflected light. To simulate such observations, we employ the 3D radiative transfer code MYSTIC, which accounts for the complexity and variability of Earth’s surface and atmosphere. To support these simulations, we developed the first hyperspectral albedo maps dataset for Earth (HAMSTER), which includes the spatial and temporal variability of surface features as a function of wavelength. Additionally, we created a novel 3D cloud generator using ERA5 reanalysis data to accurately simulate the global distribution of patchy clouds. Our results show that reproducing Earthshine observations requires detailed modeling of both cloud structures and surface albedo. These insights are critical for upcoming reflected light missions, such as the HWO, that aim to characterize Earth-like exoplanets. By refining our understanding of Earth’s radiative properties, we lay the foundation for interpreting analogous observations of distant worlds.

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Snapshots of Giant Planet Migration: case studies of eccentric warm Jupiters

November 25, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Arvind Gupta, NOIRLab

ABSTRACT
The production of Jupiter-sized planets with orbital periods of P less than 10 days – “hot Jupiters” – has presented an enticing challenge for our understanding of exoplanet dynamics and planet formation. A number of viable migration models have been put forth, but post-migration orbital evolution often erases important clues to the dynamical history of individual systems, making it difficult to determine how much each formation channel contributes to the observed population. Case studies of warm Jupiters, which will have retained primordial orbit information, offer an opportunity to tackle this challenge. I will discuss new results of an ongoing warm Jupiter observing campaign, highlighting several freshly confirmed systems, including TIC 241249530 b. This giant planet is on a retrograde orbit and now holds the crown for the most eccentric transiting exoplanet yet discovered, making it an enticing target for future transmission and emission spectroscopy studies. I will also present an analysis of the warm Jupiter mass-eccentricity distribution and implications for the dynamical history of the population.

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Hungry, Hungry White Dwarfs: Tidal Disruption of Planetesimals Post-Natal Kick

December 02, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
Tatsuya Akiba, University of Colorado Boulder
ABSTRACT
Many white dwarfs are polluted by metals, implying a recent accretion event. The tidal disruption of planetesimals is a viable source of white dwarf pollution and offers a unique window into the bulk composition of exoplanet bodies. The question of how planetary material enters the tidal disruption radius of the white dwarf, however, is unresolved. Using a series of N-body simulations, we explore the response of the surrounding planetesimal debris disk as the white dwarf receives a natal kick. We find that the kick can form an apse-aligned, eccentric debris disk in the range 30–240 au, which corresponds to the orbits of Neptune, the Kuiper Belt, and the scattered disk in our solar system. In addition, many planetesimals beyond 240 au flip to counterrotating orbits. We predict that approximately 80% of white dwarf debris disks should exhibit significant apsidal alignment and fraction of counterrotating orbits. The eccentric disk is able to efficiently and continuously torque planetesimals onto radial, star-grazing orbits. We show that the kick causes both an initial burst in tidal disruption events as well as an extended period of 100 Myr where tidal disruption rates are consistent with observed mass accretion rates on polluted white dwarfs.

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Orbital Modeling of HII 1348B: An Eccentric Young Substellar Companion in the Pleiades

December 9, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Gabriel Weible, University of Arizona
ABSTRACT
Brown dwarfs with known physical properties (e.g., age and mass) are essential for constraining models of the formation and evolution of substellar objects. In this talk, I will present new high-contrast imaging observations of the circumbinary brown dwarf HII 1348B—one of the few known substellar companions in the Pleiades cluster. We obtain the first L’-band photometric detection of the companion, enabled by direct observations taken with the Large Binocular Telescope Interferometer (LBTI). We perform precise relative astrometry of HII 1348B, leveraging the semi-independence of the two 8.4-meter apertures of the LBT. I will present the first model of the companion’s orbital motion using relative astrometry from five epochs spanning a temporal baseline of 23 years. Additionally, we fit atmospheric models to near- and mid-IR broadband photometry of HII 1348B to investigate its likely bulk atmospheric properties. By analyzing the posterior distributions of fitted orbits and model spectra, we make inferences about the possible formation scenarios and dynamical history of this hierarchical triple system.

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Spring 2024

Recent Results on Inner Disk Chemistry from the JDISCS Team

january 22, 2024   |   12 pm noon (MST)   |   Hybrid (Kuiper 309 & Zoom)
 Colette salyk,   vassar college
ABSTRACT
While the solar system provides us some information about how planetary characteristics depend on distance from the sun, many other dimensions of planet formation remain to be understood. The many dimensions of planet formation are beginning to be explored with JWST, especially using MIRI-MRS, which provides chemical information from planet-forming environments on few AU scales.  I will highlight recent results using MIRI-MRS from the JWST Disks Infrared Spectral Chemistry Survey (JDISCS) Team including: greatly improved calibration of MIRI-MRS spectra and the beautiful spectra it produces, evidence for icy pebble drift, and investigations into how stellar mass affects chemistry.  I’ll also provide a few glimpses of work in progress, and discuss how our field as a whole is moving towards probing the multiple dimensions of planet formation in future years.

Short informal talks

january 29, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Yancy shirley, shuo kong, dominia itrich, mathew murphy, kevin hardegree-ullman, serena kim

Unveiling the asymmetry of the lagrange points

february 5, 2024   |   12 pm noon (MST)   |   Hybrid (kuiper 309 & Zoom)
 augustín Alejandro heron rivas,   Pontificia Universidad Católica de Chile
ABSTRACT

In celestial mechanics, Lagrange points appear naturally in the context of the well-studied Restricted Three-Body Problem (RTBP). In particular, they are gravitational equilibrium points where the influences of two massive objects create stable regions in space. Among these points, L4 and L5, located at the vertices of equilateral triangles formed by the primary and secondary masses, have been of particular interest. These correspond to the stable Lagrange points that are expected to trap the same amount of material in their co-orbital positions in the context of planetary systems. However, both recent observations and numerical simulations have revealed a striking asymmetry between the material surrounding L4 and L5. Therefore, the goal of this talk is to present some of the physical mechanisms responsible for these interesting features. By understanding this asymmetric phenomenon, we will be able to reveal some of the key features within protoplanetary disks. For example, we could infer the presence of planets, how migration affects the evolution of planets, or the thermodynamic properties of the disk. Furthermore, these processes will be characterized by both N-body and high-resolution hydrodynamical simulations.

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Substructures in protoplanetary disk imprinted by multiple-planets and the case of HD 163296: The importance of multiple dust species in hydrodynamics

 

february 12, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 juan garrido-deutelmoser,   steward observatory

ABSTRACT

The Atacama Large Millimeter Array observations of the disk around HD 163296 have resolved a crescent-shape substructure at around 55 au. We propose that both the crescent and the dust rings are caused by a compact pair (period ratio ≃4:3) of sub-Saturn-mass planets inside the gap, with the crescent corresponding to dust trapped at the L5 Lagrange point of the outer planet. This interpretation also reproduces well the gap in the gas recently measured from the CO observations, which is shallower than what is expected in a model where the gap is carved by a single planet. The global model of the disk with four planets may fall into a long resonant chain, with the outer three planets in a 1:2:4 Laplace resonance. This configuration is not only an expected outcome from disk-planet interaction in this system, but it can also help constrain the radial and angular position of the planet candidates using three-body resonances. This numerical simulation includes the evolution of multiple dust species, and we highlight its importance presenting MDIRK: a Multifluid second-order Diagonally-Implicit Runge-Kutta method to study momentum transfer between gas and an arbitrary number (N) of dust species. In particular, admits a simple analytical solution that can be evaluated with O(N) operations, instead of standard matrix inversion, which is O(N)3. Therefore, the analytical solution significantly reduces the computational cost of the multifluid method, making it suitable for studying the dynamics of systems with particle-size distributions.  The simplicity of MDIRK lays the groundwork to build fast high-order asymptotically stable multifluid methods.

Demystifying the Sub-Neptune Frontier with JWST

february 19, 2024   |   12 pm noon (MST)   |   Hybrid (kuiper 309 & Zoom)
 anjali piette,   carnegie INstitution for science
ABSTRACT
The most common type of exoplanet detected to date lies between the sizes of Earth and Neptune – but with no solar system analogue, these ‘sub-Neptunes’ remain mysterious. Their masses and radii can be explained by a range of structures, including rocky interiors with hydrogen-rich atmospheres, water-rich magma oceans, and thick hydrospheres. Sub-Neptunes therefore provide an excellent opportunity to constrain new regimes of planetary science, and the James Webb Space Telescope (JWST) in particular is already beginning to provide new insights into these exotic planets. In this talk, I will discuss different ways in which JWST can constrain the properties of sub-Neptunes. For example, ‘lava worlds’ with dayside temperatures exceeding ~2000 K are expected to have atmospheres consisting of evaporated surface material. I will show that atmospheric observations with JWST have the power to constrain the chemical composition of this material, and discuss upcoming observations which will search for these chemical signatures. Meanwhile, JWST has already observed larger sub-Neptunes such as the hazy planet GJ 1214 b. I will discuss new constraints which we have placed on the atmospheric properties of this planet, paving the way for future studies of the sub-Neptune regime. Both current and future observatories will continue to uncover the diversity of planetary physics occurring in these enigmatic, yet common, exoplanets.

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Illuminating protoplanetary disk sub-structure and their effects on exoplanets

february 26, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 taylor kutra,   lowell observatory
ABSTRACT

Of all the areas of astrophysics, the scales involved in forming planets span the most orders of magnitude. Everything from sub-micron sized dust grains that are responsible for passively heating a protoplanetary disk, to centimeter sized pebbles which accrete to form planets, or stellar companions with separations of tens of AU, can effect the planets that eventually form. In this talk, I will describe physical processes which act on all three of these scales and describe the implications for planet formation. This includes a novel steady state for irradiated protoplanetary disks with long lived pressure bumps which may a range of implications for disk evolution and planet formation.

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Discovery of a spatially resolved disk wind and mid-IR variability: T Cha caught at the end of its evolution by JWST

march 04, 2024   |   12 pm noon (MST)   |   Hybrid (kuiper 309 & Zoom)
 naman bajaj (LPL ,U Arizona), andrew Sellek (Leiden observatory), chengyan xie (LPL, U Arizona)
ABSTRACT

Circumstellar disk dispersal is a brief, yet critical, end stage of disk evolution, dictating the end of planet formation and migration. Thermal winds powered by high-energy stellar photons have long been theorized to drive disk dispersal. However, evidence for these winds is currently based only on small (~3-6 km/s) blue-shifts in [Ne II] 12.81 um lines, which does not exclude MHD winds. We report JWST MIRI MRS spectro-imaging of T Cha, a disk with a large dust gap (~20 au in radius) and known blue-shifted [Ne II] emission. We detect four forbidden noble gas lines, [Ar II], [Ar III], [Ne II], and [Ne III], of which [Ar III] is the first detection in any protoplanetary disk. After performing continuum and PSF subtraction, we discover a spatial extension in the [Ne II] emission off the disk continuum emission, consistent with a disk wind. In contrast, we also find compact [Ar II] emission. – Naman Bajaj

We then show how by applying photoionization radiation transfer to simple hydrodynamic wind models we can predict the extent and luminosity of the Ne and Ar line emissions. Along with the low degree of ionization implied by the line ratios, we find that the relative compactness of [Ar II] compared to [Ne II] implies a dense wind such that soft X-rays and EUV only reach the inner parts of the wind while harder X-rays ionize the wind to larger radii. This requires high mass-loss rates (~10^-8 Msun/yr) and small wind launch radii (~1 au), that are consistent with the properties of X-ray-driven photoevaporation. – Andrew Sellek

We also have an unexpected discovery that the JWST continuum of T Cha is significantly different from the Spitzer data (up to 3 times lower in shorter wavelengths and 3 times higher in longer wavelengths) despite only ~17 years separating the observations. This change is highly likely to be non-periodic and can be caused by the asymmetric inner disk of T Cha that has significantly decreased in mass over human timescale. In combination with the observed disk dispersal, this inner disk evolution suggests that we might be witnessing the last stage T Cha’s disk evolution. – Chengyan Xie

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Thermal Properties of the Hot Core Population in Sagittarius B2 Deep South 

march 11, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 Desmond Jeff,   university of Florida
ABSTRACT

Hot molecular cores are thought to represent a key phase of protostellar evolution and the evolution of the ISM, as the antecedents to ultra-compact HII regions and formation sites of complex organic molecules. However, owing to the complex interplay between gas-phase and grain-surface chemistry in pre and protostellar cores, the temporal and physical evolution of hot cores is still not well understood. The evolution of hot cores is further unexplored in the Milky Way’s Central Molecular Zone (CMZ) where, owing to the CMZ’s peculiarly low star formation rate, there are few examples of ongoing star formation. We report the discovery of 9 new hot molecular cores in the Deep South region of Sagittarius B2 (Sgr B2) using ALMA Band 6 observations. LTE modeling of methanol (CH3OH) lines reveals the cores’ resolved temperature and column density structure, which we use to derive the structural properties of the cores. We further perform comparisons of these properties to a sample of hot cores elsewhere in Sgr B2 and in the Galactic disk, providing hints on the relative onset of star formation in different regions of Sgr B2, new formation pathways for CH3OH in warm (> 250 K) ISM conditions, and the impact of the CMZ’s environment on massive star formation.

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from the data to knowledge: a detailed investigation of recent findings of wasp-39b using jwst ers era

march 18, 2024   |   12 pm noon (MST)   |   Hybrid (kuiper 309 & Zoom)
 anna lüber,   Ludwig Maximilian University (LMU) University of Bern
ABSTRACT

The era of JWST transmission spectroscopy of exoplanetary atmospheres commenced with studying the Saturn-mass gas giant WASP-39b as part of the Early Release Science (ERS) program. WASP-39b was observed using four individual JWST instrument modes (NIRCam, NIRISS, NIRSpec G395H, and NIRSpec PRISM), with the resulting spectra detailed in a series of publications by the ERS team. In this presentation, we delve into assessing the information content of these spectra measured using the different instrument modes, focusing on the complexity of the temperature-pressure and chemical abundance profiles warranted by the data. We examine the detectability of molecules in each mode and discuss the fidelity of the results obtained from atmospheric retrievals. Two Bayesian inference methods are used to perform atmospheric retrievals: the standard nested sampling method and the supervised machine learning method of the random forest (trained on the model grid of Crossfield 2023). For nested sampling, Bayesian model comparison is used to identify the set of models with the required complexity to explain the data.

Feeling the Heat: testing external photoevaporation through optical forbidden lines in Orion

march 25, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 karina mauco,   European Southern Observatory
ABSTRACT

Most planetary systems, including our Solar System, form in massive star clusters, where external photoevaporation by UV radiation from OB stars profoundly influences the evolution of protoplanetary disks. The Orion star-forming region is a unique laboratory to study this process, mainly because it is the closest (~400 pc) star-forming region containing OB massive stars. 

In this talk, I will show the results of the first large-scale survey of the mid-age (~3-5 Myr) σ Orionis cluster, combining UV-IR spectroscopy and mm-continuum observations. By analyzing high-resolution optical spectra, we explore wind diagnostics through the characterization of forbidden lines, particularly the [OI] 6300 Å line. A compelling case is made for external photoevaporation mostly affecting the innermost regions, where disks exhibit remarkably low masses. 

In more hostile environments, such as the Orion Nebular Cluster, protoplanetary disks display striking teardrop-shaped clouds of ionized gas as massive stars irradiate the disk material. These objects, known as proplyds, are prime targets for studying the ionized structure of these systems. I will show the first spatially and spectrally resolved observations of 12 proplyds, taken with MUSE on the VLT. I will show striking images of the Orion proplyds, revealing their morphology across seven emission lines, and describe how the sizes of the ionization fronts and the mass-loss rates estimated for these sources confirmed the short lifetimes of the proplyds, which poses challenges for planet formation in clustered environments.

WATCH VIDEO

CO line emission supports large protoplanetary disk masses

april 01, 2024   |   12 pm noon (MST)   |   Hybrid (kuiper 309 & Zoom)
 dingshan deng, LPL, university of arizona
ABSTRACT

Carbon monoxide (CO) is one of the most abundant molecules in protoplanetary disks, and optically thin emission from its isotopologues has been detected in many disks. Surprisingly, the protoplanetary disk masses derived from CO line emission have been notably low and were inconsistent with the masses derived from other tracers. In this talk, I will discuss a new, comprehensive model that addresses the critical attributes related to CO: (a) isotope-selective chemistry, (b) freeze-out considering the grain-surface chemistry, and (c) gas density and temperature structures that are both consistent with the thermal pressure gradient. From this model, the CO line emission supports large masses in Myr-old disks. I will also present a simplified model that is capable of detailed modeling of individual targets, and its application to the disk of RU Lup. We find a disk mass larger than the Minimum Mass Solar Nebula, whereas previous estimates were around a Jupiter mass. An open-source Python-Fortran code DiskMINT (Disk Model for INdividual Targets) has also been released so that the community can extend this approach to any other disks. 

 

Super-Earths are Common in Jupiter-like Orbits

april 09, 2024 (TUESDAY)   |   12 pm noon (MST)   |   Hybrid (SO 550 & Zoom)
 weicheng zang,   cfa
ABSTRACT

Super-Earths and mini-Neptunes are absent in the relatively planet-rich Solar System, but the transit and radial velocity methods have demonstrated that they are common in short-period orbits. The standard core accretion planet formation theory predicts numerous “failed gas giant cores” in the wide orbits (>~ 1 AU), with masses of Super-Earth/mini-Neptune masses. The gravitational microlensing technique is currently the only method that can probe low-mass wide-orbit planets, but before 2020 such planets were barely detected, indicating a paucity of “failed gas giant cores”. Since 2020, I have been leading two projects to capture “failed gas giant cores”, which detected about 10 planets smaller than the detection record by 2020, suggesting that “failed gas giant cores” are common (about 1 per star). I will also introduce the statistical result from the largest microlensing planetary sample, from Earths to super-Jupiters, and the future missions for microlensing planets. 

REscheduled

april 15, 2024   |   12 pm noon (MST)   |   Hybrid (kuiper 309 & Zoom)
 sarah moran,   lpl, University of arizona
ABSTRACT

 

 

Talk1: Towards Consistent and Uniform Methods for Characterizing Scattered-Light Debris Disks: An Empirical Approach

april 22, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 justin hom,   steward observatory, university of arizona
ABSTRACT
The advancement of high contrast imaging exoplanet science through instruments such as the Gemini Planet Imager and SPHERE have provided a plethora of high resolution images of circumstellar exoKuiper belt analogues at small (<1”) scales. The enriched sample grants us the opportunity to test theories of planetary system architecture and evolution, along with providing a new regime to probe for the compositions of micron-sized dust grains, byproducts of planetesimal collisions. These new observations, however, have generated significant tensions in the way we characterize and model these systems, often leading to inconclusive and/or degenerate interpretations. Many studies also adopt uniquely tailored characterization approaches for single systems, impeding population characterization efforts. To account for this, we develop a uniformly consistent approach that leverages similar shapes in scattering phase profiles in Solar System dust observations. Using this empirically-informed scattering phase function as a proxy for all dust scattering properties, we constrain morphological properties of eight debris disks imaged by the Gemini Planet Imager without relying on scattering formalisms that suffer from limiting assumptions. We identify a diverse range of morphological properties in our sample, including structures that may be indicative of perturbations from unseen planetary companions. Reasonable fits in our modeling results for both axisymmetric and asymmetric systems also suggest that dust scattering behavior between extrasolar debris disks and the Solar System may be similar, and that this empirically-informed modeling approach may prove useful in characterizing additional dust scattering systems.

 

talk2: The Origin of Biomolecules and Information Polymers on Terrestrial Planets

april 22, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 ralph pudritz,   McMaster University
ABSTRACT
The origin of life on Earth is one of the fundamental questions of science.  A critical issue is how and when biomolecules, such as building blocks of RNA and proteins, appeared after Earth formed.  These molecules could have formed in the solar nebula or in planetesimals and delivered to early Earth during its formation.  Planet based processes include small molecule chemistry in the post impacted, reducing atmosphere of young Earth and that rained products into warm little ponds, or in undersea hydrothermal vents.  Whatever the environment, hydrogen cyanide is the basic feedstock molecule for these biomolecules (as in the famous Miller-Urey experiment) and its origin is central to the problem.  I shall discuss recent progress in pre-biotic chemistry, numerical simulations, and experiments that address these different routes to biomolecule and RNA polymer formation.  These scenarios have very different implications for the origin of life on Earth – and for the  search for life on the recently discovered, Earth-like exoplanets.

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The path towards reflected light imaging of exoplanets – 5 years of development with MagAO-X

april 29, 2024   |   12 pm noon (MST)   |   Hybrid (kuiper 309 & Zoom)
 sebastiaan haffert,   steward observatory, University of arizona
ABSTRACT

The imminent era of the Extremely Large Telescopes, like the 25-meter Giant Magellan Telescope, will offer unprecedented sensitivity and spatial resolution, enabling new discoveries in all areas of astronomy and astrophysics. Among its top priorities is the discovery and characterization of Earth-like planets that could have climates like ours and where life could form and evolve – potentially answering one of the oldest questions of humankind; are we alone? However, direct detection, and characterization, of older exoplanets is challenging due to the contrast ratio that must be overcome. Realizing such a grand goal will only be possible if we invent and implement new technologies to fulfill the ultimate potential of the ELTs. I will present the new instruments and techniques that push us forward towards the grand goal of detecting extrasolar life that I developed during my past 5 years at Steward Observatory. These new techniques have been tested with the Magellan Adaptive Optics eXtreme (MagAO-X) system, a high-contrast imaging system for the 6.5m Magellan Telescope. We use MagAO-X as a pathfinder for GMT and every improvement we make along the way allows us to do novel and improved astronomical observations.

 

 

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The complex image of star and planet formation in the harsh environment of Carina Nebula

may 06, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 dominika itrich,   alien earths team, university of arizona
ABSTRACT

Most of our knowledge about how stars form comes from the observations of the nearest star-forming regions. Their proximity allows detailed study of individual objects. However, these regions all share similar properties and therefore do not give us a representative picture of star formation in our Galaxy. Most stars form in massive complexes hosting OB stars which can significantly influence their surroundings and change the otherwise peaceful evolution of lower-mass cluster members. In particular, they produce immense amounts of UV photons which can heat and ionise outer parts of protoplanetary disks leading to removal of disk material. This process of external photoevaporation has been extensively investigated in different clusters in Orion in moderate to high UV fields. Here, I present a spectroscopic study of young stars in an extreme environment of Carina Nebula Cluster. Deep, integral field unit observations of Trumpler 14 cluster from VLT/MUSE allowed detection and characterisation of low-mass cluster members down to 0.2 Msun. We use properties of individual stars to confirm a young age of Trumpler 14. We assess accretion properties of those stars measuring CaIRT emission lines and applying empirical relations connecting line luminosities with accretion. We test how varying across the cluster UV level impacts accretion properties. We complement the investigation with measurements of forbidden atomic emission lines tracing disk photoevaporation. I will discuss our results in the context of theoretical predictions of external photoevaporation and observational studies of other star-forming sites. I will also present alternative methods of spectral classification applicable to large datasets. Our results show feasibility of deep spectroscopic studies targeting faint, low-mass sources in the distant regions enabling investigations of environmental impact on star and planet formation across wide range of physical conditions.

 

 

Multiple facets of silicate clouds in substellar atmospheres

may 13, 2024   |   12 pm noon (MST)   |   Hybrid (kuiper 309 & Zoom)
sarah moran,   LPL, university of arizona
ABSTRACT

Silicate clouds in sub-stellar atmospheres have been suspected since Spitzer observations of brown dwarfs. With the MIRI instrument on JWST, we can now more deeply probe silicate features from 8 to 10 microns, exploring specific composition, particle size, and particle structure of these potential cloud materials. Recent characterization efforts have led to the identification in particular of silicon dioxide (SiO2) cloud features in brown dwarfs, and even more recently, for the first time in a transiting giant exoplanet. Previous modeling has primarily focused on crystalline quartz or amorphous silica to match observations. I will explore the possibility of other silicates that may be more likely to form at the pressure and temperature conditions of substellar upper atmospheres. I will show how these may be observationally distinguished from each other with current JWST observations. I will also discuss how such particles could be dynamically lofted and sedimented throughout the atmosphere, and what this may mean for the underlying chemical and dynamical processes governing these objects.

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A Thermodynamic criterion for the formation of circumplanetary disks

may 20, 2024   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 leonardo krapp, university of arizona
ABSTRACT

The formation of circumplanetary disks is central to our understanding of giant planet formation, influencing their growth rate during the post-runaway phase and observability while embedded in protoplanetary disks. In this talk I will show the results from 3D global multifluid radiation hydrodynamics simulations with the FARGO3D code to define the thermodynamic conditions that enable circumplanetary disk formation around Jovian planets on wide orbits. Our simulations include stellar irradiation, viscous heating, static mesh refinement, and active calculation of  opacity based on multifluid dust dynamics. I will showcase how that the inclusion of multifluid dust dynamics favors rotational support because dust settling produces an anisotropic opacity distribution that favors rapid cooling. Finally, I will discuss potential implications of our results such as the formation of spherical isentropic envelopes around young gas giant planets, rather than circumplanetary disks.

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Fall 2023

Dust Evolution in the Dense Infrared-Dark Clouds

august 28, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 wanggi lim,   IPAC
ABSTRACT
We introduce and present the techniques and results of Mid- and Far-Infrared extinction (MIREX/FIREX) mapping methods of Milky Way infrared-dark clouds (IRDCs) that enable construction of the deepest extinction maps. IRDCs are promising sources to search for massive molecular cores which are assumed to be progenitors of high-mass protoclusters. Understanding dust grain properties in IRDCs is important to determine the initial condition of massive star cluster formation since the density structure of the molecular clouds can only be estimated in terms of absorption opacities and emissivities of dust grains at very cold temperature. In this study, we measure the spectral energy distribution of Galactic background and foreground interstellar medium of the target IRDCs and utilize the information to construct the multiband MIREX/FIREX maps. The maps allow us to investigate dust opacity variation along MIR – FIR wavelength regime where the opacity trends are sensitive to the chemical composition and size distribution of the dust grains. The comparison of the observed dust opacity trend to theoretical models constrains the best assumption of ice mantle formation and dust coagulation in each pixel position of the extinction maps. After cross-checking the trends with other physical properties, we have found evidence of dust grain growth through ice mantle formation and dust coagulation as we traverse denser and colder regions within the IRDCs. The results also indicate that the densest regions in the earliest stage of high-mass star cluster formation potentially have equivalent dust properties with inner protoplanetary disks. We will explore the implication and potential application of the results.

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NO TALK

september 4, 2023   |   12 pm noon (MST)   |   —-
LABOR DAY
 

Probing Young Planet Population with 3D Self-Consistent Thermodynamics 

september 11, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
shangjia zhang,  university of nevada
ABSTRACT

Protoplanetary disks are the birthplaces of planets. Over the past decade, there have been significant advancements in disk observations thanks to the Atacama Large Millimeter Array (ALMA) and extreme adaptive optics (ExAOs). Hundreds of disks have been observed at high angular resolutions, revealing rich substructures (e.g., gaps/rings) at various layers, some of which are perturbed by planets. A better understanding of disk physics holds great potential for unveiling more young planets within these substructures and distinguishing them from non-planet origins.

In this presentation, I will discuss how we can constrain the young planet population using statistical and machine learning techniques applied to these substructures. Additionally, I will explain the critical role of self-consistent dust and thermal structures in shaping disk morphology and kinematics, as well as why state-of-the-art radiation-hydrodynamic simulations are crucial for understanding substructures, planet formation, and the precise prediction of young planets.

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NASA’s Europa Clipper mission to study the habitability of Europa  

september 18, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Alfred mcewen,  LPL, Planetary Image Research Lab
UNiversity of arizona
ABSTRACT

With launch planned in October 2024, NASA’s Europa Clipper will explore the habitability of Jupiter’s moon Europa. Arriving at Jupiter in 2030, the spacecraft will orbit Jupiter, flying by Europa more than 40 times over a four-year period to observe this moon’s ice shell and ocean, study its composition, investigate its geology, and search for and characterize any current activity. The mission’s science objectives will be accomplished using a highly capable suite of remote-sensing and in-situ instruments. The remote sensing payload consists of the Europa Ultraviolet Spectrograph (Europa-UVS), the Europa Imaging System (EIS), the Mapping Imaging Spectrometer for Europa (MISE), the Europa Thermal Imaging System (E-THEMIS), and the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON). The in-situ instruments comprise the Europa Clipper Magnetometer (ECM), the Plasma Instrument for Magnetic Sounding (PIMS), the SUrface Dust Analyzer (SUDA), and the MAss Spectrometer for Planetary Exploration (MASPEX). Gravity and radio science will be achieved using the spacecraft’s telecommunication system.  The spacecraft and payload are currently nearly complete, and system testing is underway. The Jupiter tour is complete, and work is beginning on detailed science planning to achieve the science objectives, which require multiple science instruments.  The project has a “one science team” philosophy, which will be an interesting experiment for this type of mission.  There are extensive plans for inclusion of a diverse community.  

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A multiwavelength perspective on planet formation conditions

 

september 25, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
catherine espaillat, Boston University
ABSTRACT

We know that protoplanetary disks surround many pre-main-sequence stars, but how these systems evolve into planetary systems is a fundamental question in astronomy. Multiwavelength studies of these variable young stars can provide insight into the star-disk connection and the conditions under which planets form. This talk will review key observations of protoplanetary disks and their young stars, focusing on multiwavelength observations and variability. I will discuss variable high-energy radiation fields generated by the accretion process (traced in the UV and optical) and disk masses and structures observed at longer wavelengths (in the IR and mm).  To conclude, I will discuss possibilities for future progress in multiwavelength time-domain studies of these young systems. 

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Talk 1: Observations of Exoplanet Atmospheres, from the Ground and from Space

Talk 2: Bioverse and the Prospects for Observing Biosignatures

 

october 02 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Alien earths team,   university of Arizona

 Megan Mansfield (U Arizona/Steward Obs) & Kevin Hardegree-Ullman (U Arizona/Steward Obs)

ABSTRACT1
In this talk, I will review recent developments in observational characterization of exoplanet atmospheres using both ground-based and space-based observations. I will present some results from the JWST Transiting Exoplanet Early Release Science program, and I will discuss the recent development of the technique of spectroscopic eclipse mapping. I will also discuss recent advances in measuring atmospheric compositions using ground-based, high-resolution instruments, including how these observations are giving us new ways to probe planetary formation pathways. Finally, I will discuss future possibilities for studying exoplanet atmospheres with the next-generation Extremely Large Telescopes.
ABSTRACT2

 

New and upcoming space and ground-based facilities aim to deliver the first true measurements of biosignatures on rocky habitable zone planets. Recent studies have concluded JWST should be able to detect certain biosignatures such as CO2 and CH4 under the right exoplanet atmospheric conditions, but key biosignatures such as O2 will not be detectable. The collecting area, sensitivity, and wavelength coverage afforded by the ELTs make them the perfect platform to complement observations with space telescopes and can significantly increase our ability to detect biosignatures. We developed Bioverse, an open-source modular framework to simulate surveys, test hypotheses, and perform trade studies to assess the capabilities of upcoming and future facilities to detect exoplanet features such as biosignatures and address population-level questions. Our recent Bioverse simulations with the ELTs go beyond previous studies and account for constraints such as planet occurrence rates, relative system velocities, and target observability. I will present our new simulations, which predict whether or not Earth-like levels of O2 could be probed on Earth-sized exoplanets within 20 pc of the Sun, including the TRAPPIST-1 system. Bioverse, and the new capabilities added by our project, now enables realistic, systematic assessment of which hypotheses about habitable exoplanet atmospheres will be testable by joint constraints from the ELTs and new space facilities.

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The ongoing hunt to detect the radio emissions of exoplanets 

october 09, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)

jake turner ,  cornell university

 

ABSTARCT

One of the most important properties of exoplanets has not yet been directly detected despite decades of searching: the presence of a magnetic field. Observations of an exoplanet’s magnetic field would yield constraints on its planetary properties that are difficult to study, such as its interior structure, atmospheric escape and dynamics, and any star-planet interactions. The presence of magnetic fields on gas giants also affects the understanding of their origins and evolution. Additionally, magnetic fields may contribute to the habitability of terrestrial exoplanets. Observing planetary auroral radio emission is the most promising method to detect exoplanetary magnetic fields. 

In this talk, I will present our recent study of the Tau Bootis exoplanetary system where we have the first possible detection of an exoplanet in the radio using LOFAR (Turner et al. 2021).  Assuming the emission is from the planet, we derived a maximum surface polar magnetic field for tau Boo b between ~5-11 G. The magnetic field and emission strengths we derived are consistent with theoretical predictions, and if this detection is confirmed it will place important constraints on dynamo theory, comparative planetology, and exoplanetary science in general. Additionally, I will present the first results of an extensive multi-site follow-up campaign to confirm the radio detection of tau Boo b. Our first observing campaign consists of low-frequency radio data taken simultaneously from NenuFAR and LOFAR. Preliminary analysis of this data show no signs of emission. Therefore, the original signal may have been caused by an unknown systemic or we are observing variability in the planetary radio flux due to observing at different parts of the stellar magnetic cycle. Our second follow-up observing campaign is designed to test the latter conclusion. We have coordinated observations of the magnetic maps of the host star alongside many months of intensive radio monitoring by NenuFAR. Preliminary results on the second campaign will be presented. Finally, I will briefly highlight the promising landscape of studying exoplanetary magnetic fields in the coming decades with future ground- and space-based radio telescopes

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The Value of a Gibbous Asteroid: Connections between Phase Curves and Asteroid Taxonomy

october 16, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Zachary Murry,  harvard university
ABSTRACT

The relationship of an asteroid’s magnitude to its phase has a long history of study including efforts to study the correlation between these parameters and spectral type. However, these efforts often suffer from the inclusion of only a few asteroids, missing phase curve data, uncorrected rotational or apparitional aberrations, and other issues. We take a closer look at the problem and figure out how much information about an asteroid’s spectral type is contained in its phase curve.

Characterizing the climates of temperate rocky exoplanets in the era of JWST

october 23, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Tad Komacek,  university of maryland
ABSTRACT

The advent of JWST has enabled the first broadband spectroscopic studies of rocky exoplanets orbiting nearby stars. JWST will provide an opportunity to potentially constrain the atmospheric composition of rocky exoplanets that lie within the habitable zones of low-mass stars. However, such observational characterization via transmission spectroscopy may be formidable due to challenges associated with stellar activity, atmospheric loss, and high-altitude clouds and hazes. In this talk, I will discuss recent efforts to determine the extent that clouds and time-variability impact the transmission spectra of temperate rocky exoplanets orbiting M dwarf stars. To simulate the impact of clouds on the climate state and observable properties of rocky exoplanets, we use the ExoCAM GCM post-processed with the Planetary Spectrum Generator (PSG) Global Emission Spectra (GlobES) radiative transfer code. I will present simulations of 3D climate, atmospheric variability, and transmission spectra both for idealized systems of rocky exoplanets orbiting M dwarf stars, as well as the best habitable zone candidate for observational characterization, TRAPPIST-1e. By applying a novel dynamical systems framework, we find that many properties of the climate dynamics of TRAPPIST-1e are analogous to that of Earth, but the planet is strongly discrepant to Earth in its extreme climate behavior. We find that TRAPPIST-1e both undergoes amplification of nightside temperature (similar to polar amplification on Earth) and increasing high-altitude variability with increasing greenhouse gas complement. We also find that cloud coverage does not prevent detection of both the key habitability indicator water vapor as well as the potential carbon dioxide-methane biosignature pair in the atmosphere of TRAPPIST-1e over the nominal lifetime of JWST. This implies that searching for disequilibrium biosignature pairs in the atmospheres of temperate rocky planets orbiting nearby low-mass stars may be feasible in the coming decade.

 

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JWST as a Linchpin for Circumstellar Disk Science

october 30, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Schuyler Wolff,  steward observatory, university of arizona
ABSTRACT

Since the discovery of the “Vega Phenomenon” with IRAS, circumstellar disks have been a growing field of study for their ability to serve as signposts for both stellar and planetary system evolution. The infrared is ideally suited to observe these systems where thermal emission from the dust peaks and solid state spectral features can elucidate the dust properties. JWST allows for unprecedented spatial and spectral resolution in the near to mid-IR and has already changed our view of several archetypal disk systems. I will present results from several disk-focused JWST GTO programs using both scattered light observations with NIRCam coronagraphy and thermal emission with MIRI. In a broader context, I will discuss the potential impact of JWST on our understanding of circumstellar disk physics and how it complements past and future observatories. 

AI4Astro: Exploting star formation and ISM through artificial intellicence

november 06, 2023   |   12 pm noon (MST)   |   Hybrid (So n305 & Zoom)
duo xu,  university of virginia
ABSTRACT

TBAMachine learning, particularly deep learning, is transforming astronomy by enabling efficient processing of large datasets. Deep learning surpasses human capabilities in rapidly and accurately analyzing complex data such as images and data cubes in the field of the interstellar medium and star formation. Denoising diffusion probabilistic models (DDPMs) are machine learning algorithms inspired by diffusion thermodynamics, demonstrating state-of-the-art performance in various domains. DDPMs offer several advantages as tools for inferring physical quantities in astronomy, including stable training, robust performance, interpretability, and alignment with the inherent nature of scientific problems. In this talk, I will introduce applications of DDPMs to infer intrinsic physical quantities, such as volume density and interstellar radiation field, from observational data. I will also introduce how DDPMs can be used for segmentation tasks, such as segmenting filaments from dust emission.

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Gas-Rich Debris Disks’ Origins in Slow Photoevaporation Around Intermediate-Mass Stars

november 08, 2023 (WEDNESDAY SPECIAL TALK)   |   12 pm noon (MST)   |   Hybrid (TBA & Zoom)
Ryohei nakatani,  NASA/JPL
ABSTRACT
In the study of planet formation, a key goal is understanding how protoplanetary disks (PPDs) evolve into systems of planets and debris.  Traditionally, PPDs are thought to last no more than 10 million years (Myr), as inferred from infrared, Hα, and UV observations.  This age marks the transition from gas-rich PPDs to gas-free debris disks.  However, recent observations have revealed about 20 debris disks harboring gas, despite ages exceeding 10 Myr.  These gas-rich debris disks are found most often around A-type stars up to 50 Myr old.
Our new radiation hydrodynamics simulations demonstrate that PPDs’ gas can persist beyond 10 Myr around A stars if the disks become depleted of small grains compared to the interstellar medium.  In such cases, photoevaporation operates slowly due to inefficient photoelectric heating and the host stars’ weak EUV and X-ray emissions.  The model also predicts disk lifetimes that align with the observed incidence of gas-rich debris disks versus host star mass.  These results suggest many of the gas-rich debris disks are long-lived protoplanetary disks, contradicting the common wisdom that the gas was released much more recently from asteroids or comets.
Apart from our new study above, I will also additionally talk about molecular photoevaporative winds observed in the self-consistent radiation hydrodynamics simulations of my previous studies.  

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A MANATEE Dive into Hot Jupiters with JWST

november 13, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Everett Schlawin,  steward observatory, University of arizona
ABSTRACT

Transmission and emission spectra give insights into the composition, temperature structure, aerosols and formation of giant planets. The MANATEE survey probes the atmospheres of giant planets and extends from warm planets, where methane is expected to be a significant carbon reservoir to hot planets where carbon monoxide is a significant carbon reservoir, permitting study of the chemistry and physics of these planets. We will focus on two hot Jupiters: WASP-80 b, which has methane throughout its atmosphere and WASP-69 b, for which obtain new view of the dayside with a JWST emission spectrum to 2.1 to 11 microns. WASP-69 b’s atmosphere is enriched in heavy elements compared to solar composition, as evidenced by its carbon dioxide, carbon monoxide and water vapor content. We also find an unexpectedly high planet-to-star flux ratio at short wavelengths, indicating a possible influence of clouds either by reflecting light or modifying the temperature structure. These JWST spectra open a new window into hot Jupiter atmospheres in the sub-1000 K temperature regime where chemical transitions and aerosol formation can occur.

constraining the physical properties and volatile contents of the original planetesimals

november 20, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
bryce bolin,  NASA GSFC

ABSTRACT
Small solar system bodies can be broadly separated into two groups: a.) those that accrete directly from the protoplanetary disk and b.) those that are fragments produced by the collisional disruption of a larger parent body. Fragments in the solar system’s Main Belt fragments disperse in physical space over time due to secular gravitational and non-gravitational effects, however, remain linked by their orbital and physical parameters. We have developed a technique with the capability of identifying a group of asteroids as collisional fragments based on correlations between their physical and orbital parameters. This technique was used to discover >4 Ga-old asteroid families in the inner MB revealing asteroids with D > 35 km that do not belong to any asteroid family implying that they originally accreted from the protoplanetary disk and support recent theories on the formation of planetesimals. In addition, we study the volatile contents of a ~140 km diameter comet, C/2014 UN271, large enough that it could be an intact example of a planetesimal that formed in the protoplanetary disk. UN271 is on its first inward journey into the solar system’s planetary region from the Oort cloud implying that its volatile contents may be preserved since the accretion of the parent body in the protoplanetary disk. We present JWST/NIRSpec prism IFU observations of UN271 between 0.6-5.3 microns providing coverage of cometary ice and gas features and their production rates. We will discuss the implications for the timing of the formation of the original planetesimals as well as UN271’s formation environment within the protoplanetary disk.

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Atmospheric Chemical Reaction Network Topology as a Potential Biosignature for Exoplanets

november 27, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Theresa Fisher , Alien earths team,  EEB, University of arizona

ABSTRACT

With the ability to potentially observe the atmospheres of exoplanets via transit spectroscopy on the near-term horizon, the possibility of atmospheric biosignatures has received considerable attention into astrobiology. While traditionally the field was focused on biologically relevant trace gases such as O2 and CH4, this approach has raised the specter of false positives. Therefore, to address these shortcomings, a new set of methods is required to provide higher confidence in life detection. 

One possible approach is measuring the topology of atmospheric chemical reaction networks (CRNs). To assess the use of CRNs as biosignatures, a large number of  terrestrial worlds were modeled, divided into two categories: Anoxic Archean Earth-like planets that varied in terms of methane surface flux (featuring either biotic or abiotic sources), and modern Earth-like planets with and without a surface flux of CFC-12 (to represent the presence of industrial civilizations). Atmospheric CRNs were constructed from the converged models and analyzed their topology, finding that network metrics provided greater constraints on the presence of life or technology, particularly in the case of the Archean Earth models. These results suggest that atmospheric CRN topology can provide a lower risk of false positives in detecting exoplanet biosignatures.

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Decoding Exoplanet Atmospheres: The Revolutionary Role of JWST

december 04, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Luis Welbanks, arizona state university 
ABSTRACT

The 2020s and beyond will be the era of spectroscopy of exoplanet atmospheres. In just 2 years, our field has made dramatic advancements, moving from having very limited wavelength coverage and precision data from the Hubble Space Telescope (HST), to having high-precision spectroscopy over a wide wavelength range (~0.4 to 20μm) with the James Webb Space Telescope (JWST). These exquisite observations come with the opportunity to perform detailed reconnaissance of exoplanet atmospheres, explore their chemical and physical properties, and perform population-level studies to test our hypotheses for planet formation and evolution.

In this talk, I will share with you the advancements ushered by the era of JWST, allowing us to answer not only what exoplanet atmospheres are made of, but also which data drive our inferences and how reliable these inferences are. I will present the results from several programs with JWST. In these programs, we detect and constrain several chemical species that were previously elusive in exoplanetary atmospheres, including methane (CH4), ammonia (NH3), sulfur dioxide (SO2), carbon monoxide (CO), and carbon dioxide (CO2), alongside several precise water (H2O) measurements. The atmospheric retrievals performed on these data provide insights into the dynamics, chemistry, and climatic conditions of these distant worlds, as well as their metallicities. They also provide the relative elemental ratios (C/O, N/O, N/S) necessary to better understand the formation and evolution pathways of planetary systems.

I will present our progress in robustly and accurately processing JWST Time-Series Observations data. Additionally, I’ll discuss modeling advancements and our methods for reliably inferring the complete chemical inventory of our diverse exoplanet sample. Our findings underscore the transformative power of JWST and pave the way for future, in-depth atmospheric investigations of a larger exoplanet population.

TBA

december 11, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
OPEN

ABSTRACT

TBA

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Spring 2023

finding atmospheres on m dwarf terrestrial planets with jwst

january 23, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
megan mansfield,  
alien earths team, Steward observatory, U Arizona
ABSTRACT

The launch of JWST in December 2021 opened up a new realm of transiting planets to atmospheric characterization. For the first time, we will have the necessary sensitivity to study detailed spectra of terrestrial planet atmospheres and begin to search for gases that could indicate a planet suitable for life. However, there remain several unknowns about terrestrial planets orbiting M dwarfs. A first order question in our search for habitable exoplanets is whether M dwarf planets hit with intense stellar radiation could hold onto atmospheres long enough to develop life. In this talk, I will first give a broad overview of the first exoplanet results from JWST and its expected capabilities for characterizing terrestrial planets. I will then present a method of using JWST to quickly determine which M dwarf planets host atmospheres by measuring secondary eclipse photometry with the Mid-Infrared Instrument (MIRI). Finally, I will discuss how this method will be applied in JWST programs later this year.

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HALPHA: an HST search for accreting protoplanets in transition disk gaps

january 30, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 Yifan zhou,   University of texas, Austin
ABSTRACT
The direct-imaging detections of accreting young planets open up a new era of planet formation studies. These observations allow us to witness how planets assemble, constrain planets’ mass accretion processes, and understand the interactions between planets and their natal environment. Hubble Space Telescope (HST) naturally obtains high-Strehl-ratio images over a broad wavelength range, particularly the optical and ultra-violet (UV) bands where planetary spectra show accretion signatures. This capability offers exciting opportunities to discover and characterize accreting planets. Recently, we embarked on the Hubble Accreting Luminous Protoplanets in H-Alpha (HALPHA) Survey to search for accreting planets in gaps of transition disks. I will present the survey’s motivation, design, and early results. I will also describe the follow-up effort in validating the protoplanet candidate AB Aur b. The exquisite high-contrast images collected by our survey create numerous collaboration opportunities for investigating the formation and evolution of giant planets.

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Atmosphere of an Accreting planet in Realistic Global Disk Models

february 6, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 leonardo krapp,  Steward observatory, U arizona
ABSTRACT

Giant planet formation leads to two distinct classes of planets: gas giants like Jupiter whose mass is dominated by their gaseous envelope and ice giants where a much smaller envelope overlays a rocky or icy core of several Earth masses. What process halts the growth of ice giants and determines their final mass and composition is currently under hot debate. In this talk, I will present 3D multi-fluid hydrodynamics simulations of a planet embedded in a disk. I will focus on realistic cooling calculations with opacity based on self-consistent dust dynamics. In particular, I will showcase the regimes where the opacity of the planet envelope deviates from spherical symmetry, and therefore it may not be trivially cast in 1D models. This is critical to assess the scope of the leading core accretion theory and explain the exoplanets demographics.

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Constraining the Evolution of Protoplanetary Disks in Clustered Star-formation Environments

february 13, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Ryan boyden,  alien earths team,Steward observatory, U arizona
ABSTRACT

Protoplanetary disks are the birthplaces of planetary systems, and obtaining a complete picture of how planets form hinges on an understanding of how disks evolve throughout the Galaxy. The Atacama Large Millimeter Array (ALMA) and Karl G. Jansky Very Large Array (VLA) provide the sensitivity and resolution needed to detect large samples of protoplanetary disks in young stellar clusters, the most common sites of star formation in our Galaxy. In this talk, I will present the analysis of deep, high-resolution ALMA CO(3-2) and HCO+(4-3) observations covering a large sample of disks in the Orion Nebula Cluster (ONC). I first introduce the sample of disks that are detected in the observations, and then outline a novel procedure that utilizes thermochemical and line radiative transfer modeling to constrain the total disk masses, gas-to-dust ratios, and central stellar masses of the detected sources. I find that the ONC disks are massive and compact, with typical radii <100 AU, gas masses >1 Jupiter mass, and gas-to-dust ratios >=100. The ISM-like gas-to-dust ratios derived from thermochemical modeling suggest that compact disks in the ONC are less prone to gas-phase CO depletion than the massive, extended disks that are commonly found in lower-mass star-forming regions. The presence of massive gas disks indicates that a subset of disks in the ONC still have plenty of material to form giant planets, despite ongoing environmental effects. Finally, I will discuss my recent work with the VLA to constrain the free-free emission spectra and complete the census of ‘proplyds’ towards young stellar objects in the Orion NGC 1977 and NGC 2024 clusters.

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Talk is CANCELLED

 

february 20, 2023 | 12 pm noon (MST) | Hybrid (SO N305 & Zoom)
logan pearce, steward observatory, U arizona
ABSTRACT

I will present an overview of several observational projects using high contrast imaging to probe planetary regimes of stars, particularly those with wide stellar companions. I will describe the unique utility of wide binaries in direct imaging observations and data reduction through the Binary Differential Imaging technique (BDI), and a new stellar binary discovered using BDI and astrometry with MagAO and MagAO-X. I will briefly discuss the MagAO-X extreme adaptive optics instrument, its current status and science goals, and two new direct imaging surveys I am conducting with MagAO-X: a white dwarf-main sequence binary survey and an accelerating stars survey. Finally I will discuss the follow-on instrument GMagAO-X for the Giant Magellan Telescope and a project I am beginning with collaborators at NASA Ames on modeling planets in reflected light imaging with GMagAO-X.

Revealing the population of forming giant planets (special talk)

 

february 22, 2023   |   12 pm noon (MST)   |   Hybrid (SO 550 & Zoom)
Gabriele Cugno, University of Michigan
ABSTRACT

During the last years (sub-)mm and high contrast imaging observations have targeted dozens of circumstellar disks, revealing a breathtaking diversity in substructures like gaps, spirals, etc. It is thought that at least some of the observed structures are related to the formation of protoplanets. To test this hypothesis, in the past years the NaCo-ISPY large program collected deep high-contrast imaging data of more than 50 young protoplanetary disks. This is the largest existing survey uniquely focused on this type of objects and it provides a great opportunity to reveal young objects embedded in disks and statistically characterize their population.  In this talk, I will present the newest results from the ISPY protoplanetary disks survey, including the detection of known and new companions and disks. In addition, detection limits were obtained, providing strong constraints on which planet architectures could exist and on the overall giant planet population around young stars. 

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Characterizing Brown Dwarfs and Exoplanets in the Mid-Infrared

february 27, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
brittany miles,  steward observatory, U Arizona
ABSTRACT

Brown dwarfs are high-quality testing grounds for atmospheric models and optimizing requirements for exoplanet-focused instrumentation. Brown dwarfs have similar atmospheric physics and chemistry to gas giant exoplanets, but are much easier to observe because they do not suffer from host star obscuration. I will discuss observational projects to characterize disequilibrium chemistry and cloud properties in the atmospheres of brown dwarfs in different effective temperature ranges. First, I took 3 – 4 micron spectra of VHS 1256b and PSO 318.5, two analogs of the HR 8799 planets using Keck/NIRSPEC. We detected depleted methane features, providing evidence of atmospheric disequilibrium chemistry. For my second project, we acquired Gemini/GNIRS 4.5 – 5 micron spectra of four ultra-cool brown dwarfs. Combined with previously existing mid-infrared spectra of four additional brown dwarfs I show that brown dwarfs 700 K and below have disequilibrium carbon monoxide absorption. Lastly, I will share the results of the JWST Early Release Science observations of VHS 1256b which cover 1 to 20 microns at medium resolution and show detections of water, methane, carbon monoxide and silicate cloud features. 

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No Talk

march 6, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)

University of Arizona Spring Recess

Revealing Atmospheric Trends on Irradiated Brown Dwarfs with Phase-resolved HST/WFC3 Spectroscopy

march 13, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Rachael amaro,  steward observatory, u arizona
ABSTRACT

Brown dwarfs in tidally-locked orbits around white dwarfs offer an exciting opportunity to explore properties of irradiated atmospheres. These highly irradiated brown dwarfs have ultrashort rotation periods (<2 hours), weak to strong internal heat flux, and intense external irradiation, making them an ideal testbed for investigating the importance of these parameters on key atmospheric processes. In this talk, we will present high-quality, phase-resolved HST/WFC3 spectroscopy from 1.1 to 1.7 microns of the binary system NLTT5306, a ~1700 K brown dwarf in a ~102 minute orbit around a white dwarf. With this brown dwarf, our team addressed two key questions driving atmospheric studies: (1) understanding the structure and formation/disruption of clouds under the presence of intense, tidally-locked irradiation, and (2) characterizing the efficiency of day-to-night heat redistribution. Finally, we end with an overview of the constraints on cloud cover and atmospheric dynamics in four irradiated brown dwarfs, exploring trends with irradiation level, temperature, and rotation period.

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Prebiotic Chemistry in Hydrothermal Systems on Early Earth and Ocean Worlds

march 20, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Laurie Barge,  JPL
ABSTRACT

It is theorized that life on Earth could have begun at seafloor hydrothermal vents – if so, this also provides a possible way for life to emerge on ocean worlds such as Saturn’s moon Enceladus which may host hydrothermal systems. However, hydrothermal vents on Earth host a variety of chemical conditions, which can result in different outcomes of prebiotic organic reactions. In this talk I will discuss our group’s work on simulating prebiotic hydrothermal chimneys and sediments, and the organic chemistry that can occur within. Particularly I will present results from our recent studies investigating how changing geochemical conditions can lead to different prebiotic reactions, and discuss different types of vents in which these conditions may be found. Our origin of life investigations aim to bridge the gap between geochemistry and biochemistry in an early Earth context, as well as to inform the search for life and its origin on other planets.

 

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Coupling interior, atmosphere and microbial growth models to assess habitability and predict biosignatures

march 27, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Antonin Affholder, 
alien earths team, steward observatory, u arizona
ABSTRACT

What constitutes evidence that an extraterrestrial environment could be habitable to certain organisms? What constitutes a clue that a biosphere might exist on a planet or a moon?

To tackle those questions, one must lay out the theoretical basis that can (i) assess whether certain conditions permit viability of a population of given organisms and (ii) couple the dynamics of such a population to geochemical processes that together shape the value of quantities measurable remotely: observables.In this Origins Seminar, I will describe how we modeled a hypothetical population of methanogens at Enceladus’s seafloor to assess the habitability and biosignatures of the icy Saturnian moon. Next, I describe how ongoing work aims to port this inference approach to assessment of habitability and biosignatures of terrestrial exoplanets using atmospheric spectrum. 

Radio Perspectives on Star-Planet Interactions

april 3, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
melodie m. kao,  UC Santa cruz, ASu
ABSTRACT

Planetary magnetic fields influence atmospheric evaporation from space weather, yield insights into planet interiors, and are essential for producing aurorae. The most direct way of measuring magnetic fields on exoplanets and their brown dwarf cousins is by observing their magnetospheric radio emission.  Low-frequency radio arrays will soon be sensitive to exoplanet radio emission and provide a new means of exoplanet detection and characterization. Now is a critical time to prepare for these upcoming searches by harnessing detailed studies of radio emission on observationally accessible exoplanet analogs: planetary-mass and cold brown dwarfs. I will synthesize the state of the art for radio star-planet interactions as well as brown dwarf magnetospheric radio studies, discuss implications for exoplanet magnetism, and highlight opportunities for the next generation of ground- and space-based radio facilities.

Life in the Light: Photochemical Insights Towards Life as a Planetary Phenomenon

april 10, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
sukrit ranjan,  LPL, University of arizona
ABSTRACT

Advances in origins-of-life chemistry are transforming our understanding of how life emerged on Earth, while upcoming space missions offer the prospect of detecting life on other worlds. Fundamental to both quests is interaction of UV radiation with molecular systems (photochemistry). Photochemistry controls the chemical context for the origin of life on Earth and influences the molecular signposts with which we hope to detect life elsewhere. I will share photochemical work which refines our understanding of early Earth environments, and demonstrate how such understanding enables assessment and improvement of theories of origins-of-life chemistry. I will discuss photochemical efforts to elucidate potential atmospheric biosignatures of life on other worlds, and show how the search for life on other worlds may enable tests of theories of the origin of life. In sum, I will review theoretical, experimental, and observational work towards understanding the origin and distribution of life in the universe through the lens of photochemistry.

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Using ancient meteorite inclusions to constrain dynamics in the protoplanetary disk

april 17, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
emilie dunham,  ucla

ABSTRACT

Ancient particles found in meteorites called calcium-aluminum-rich inclusions (CAIs) were the first-formed solids in the hot inner region of the Solar System and can be used as tracers of movement in the solar nebula disk. Carbonaceous chondrites (CCs) contain abundant CAIs but are thought to have accreted in the outer Solar System, requiring that CAIs must have been transported outward. Curiously, CAIs are rare in ordinary, enstatite, and rumuruti chondrites, non-carbonaceous chondrites (NCs), that likely formed in the inner Solar System. In this presentation, I will address whether the hypothesis of an early-formed proto-Jupiter “opening a gap” in the disk can explain the dichotomy in the relative abundance of CAIs in CC and NC chondrites. To do this, I will explore the abundance, size, and mineralogy of 232 new NC CAIs as well as Al-Mg and oxygen isotope systematics of a subset of these. We find that, though NC CAIs are less abundant (0.01 area%), smaller, and have less melilite than CC CAIs, both NC and CC CAIs have similar isotopic characteristics. Together, this suggests that NC and CC CAIs formed in the same environment over a ~400,000 year time period, that CAIs were transported outwards by disk diffusion, and that the proto-Jupiter gap trapped CAIs in the outer Solar System. 

 

Nearby young moving groups: improvement on membership evaluation and the age of the beta-Pictoris moving group

april 24, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
jinhee lee,  kasi, Korea  & steward observatory (KASI-arizona fellow)

ABSTRACT

Nearby, young moving groups (NYMGs) are loose stellar associations with mean distances of smaller than 100 pc from the Sun. The proximity and youth of the NYMGs have placed the NYMGs a unique position in studies of stellar, substellar, and exoplanet astrophysics. For example, the NYMG members have been prime targets for the direct imaging of exoplanets. To fully take advantage of the usefulness of these NYMGs, the properties of NYMGs should be well defined. Numerous searches to NYMG members increase the number of identified members, and there are heterogeneities in member selection criteria that may cause confusion in membership status. It links to the properties of NYMGs and related studies such as planet mass estimation from direct imaging. In this talk, I will introduce an NYMG membership calculation tool BAMG (Bayesian Analysis of Moving Groups) developed by our research group. I will also present an age estimation study of the beta-Pictoris moving group using traceback methods. Finally, I will introduce our project of exoplanet survey using Gemini/IGRINS and a planned project of target preparation for direct exoplanet imaging survey preparing the GMT era.

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The distribution of volatile elements during rocky planet formation, a laboratory perspective

may 1, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Terry-Ann Suer, 
Laboratory For Laser Energetics, University of Rochester and Steward Observatory. 
ABSTRACT

Understanding the accretion and distribution of highly volatiles elements (HVEs: H, C, N, S) during planet formation is crucial for studies of habitability. With the recent expansion in the inventory of rocky planets by exoplanetary surveys, much effort is going into modeling planet formation and evolution with particular emphasis on atmospheres. In addition to being major atmospheric components, volatile elements can also get sequestered into metallic cores and silicate mantles during differentiation. Distribution coefficients and solubilities of volatile elements between major planet forming reservoirs are therefore key inputs for the models being used to connect the astrophysical observables with surface and interior processes. Recent works have focused on investigating the effects of pressure, temperature and redox on the metal-silicate and magma-gas exchange coefficients for the HVEs. I will present major recent results from these laboratory works and theirapplication to quantifying distribution of HVEs in bodies of sizes from planetesimals to the Earth. The limitation of the current dataset for modeling bodies larger than the Earth will be discussed. I will also present preliminary experimental results on the effects of deep terrestrial magma ocean conditions on the interpretation of geochemical signatures, particularly those relevant to volatile accretion chronology.

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The Quest for Exoplanet Oxygen with Extremely Large Telescopes

may 8, 2023   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Kevin Hardegree-Ullman,  
alien earths team, steward observatory, u ariozna

ABSTRACT

Molecular oxygen is a strong indicator of life on Earth and may indicate biological processes on exoplanets too. Recent studies proposed that Earth-like O2 levels might be detectable on nearby exoplanets using high-resolution spectrographs on future extremely large telescopes (ELTs). However, these studies did not consider constraints like relative velocities, planet occurrence rates, and target observability. I will discuss our new comprehensive calculations accounting for these additional constraints. We updated and used the Bioverse framework to simulate a survey of M dwarfs within 20 pc to determine if it will be practically feasible to probe for Earth-like O2 levels on transiting habitable zone Earth analogs via transmission spectroscopy with the ELTs.

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Bioverse and the habitable zone hypothesis

may 15, 2023   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
Martin Schlecker,  
alien earths team, steward observatory, u arizona

ABSTRACT

The study of planetary habitability has become a major emerging research area, with critical implications for the future of exoplanet exploration and ambitious ground- and space-based telescope missions. Yet, habitability remains challenging to determine for individual planets. My talk focuses on comparative planetology as a means to overcome some of these challenges. I will discuss comparisons of planet population syntheses with exoplanet demographics that illuminate the requirements for habitable terrestrial planets, including the role of giant planets for their water inventory. I will further present Bioverse, a quantitative framework for assessing the diagnostic power of next-generation exoplanet surveys, and its application in testing the habitable zone hypothesis. Specifically, we explored the requirements for a mission to probe and characterize its inner edge: the runaway greenhouse transition. It appears that this first empirical test of the habitable zone concept may be imminent. It will help to guide the search for extraterrestrial life in the Universe.

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BACK TO TOP

Fall 2022

Volatile chemistry in planet-forming disks

august 29, 2022   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
 jennifer bergner,   Alien earths team, University of Chicago
ABSTRACT

Planets form within disks composed of gas, ice, and dust in orbit around young stars. The distribution of volatiles (gas+ice) within these disks profoundly impacts both the chemical and physical outcomes of planet formation– including the delivery of prebiotic building blocks to new worlds.  In this talk, I will highlight our recent advances in disentangling how organic complexity is built up during the star and planet formation sequence, the role of interstellar inheritance in setting disk volatile compositions, and the distinctive volatile chemistry at play during the planet formation epoch.  These insights are gained by combining telescope observations, ice chemistry experiments, and disk simulations, each of which contributes an indispensable piece of the puzzle.  Taken together, we are assembling a more complete picture of the chemical environment which regulates the formation, composition, and potential habitability of planetesimals and planets 

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lfast, the large fiber array spectroscopic telescope

september 06, 2022 (TUESDAY)   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
roger angel,   Steward observatory, U Arizona
ABSTRACT

The LFAST concept is to use thousands of small telescopes combined by fibers for high resolution spectroscopy (R=100,000 – 150,000), in a way that will realize large cost savings and lead ultimately  to an affordable ($1B) aperture of 20,000 m2. Such large aperture is needed, for example, to make a comprehensive search for biosignatures in the atmospheres of transiting exoplanets.

Each unit telescope of 0.76 m aperture (0.43 m2) will focus the image of a single star onto a fused silica fiber, subtending 1.32 arcsec. Our telescope design calls for a spherical mirror, with a 4-lens assembly at prime focus that corrects not only for spherical aberration, but also for atmospheric dispersion down to 30° elevation and for rapid image motion caused by seeing or wind jitter. A method for rapid production of such mirrors has been tested, in which a disc of borosilicate float glass is slumped over a high-precision polished mandrel to an accuracy that greatly reduces subsequent optical finishing time. For the first LFAST array, 1,200 m2 in collecting area, the telescopes will be mounted in the open in groups of 20 located 12 m apart., some 150 m in diameter, with a total of 132 mounts and 2,640 mirrors. The light from all the fibers will be combined at two central echelle spectrographs. Together, these cover simultaneously the spectral range 390 nm – 1700 nm. The targeted cost for this first installed LFAST telescope and fiber array is $60M.

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Probing protoplanetary disk evolution using multi-wavelengths observations

september 12, 2022   |   12 pm noon (MST)   |   Hybrid (LPL 309 & Zoom)
marion Villenave,   JPL 
ABSTRACT

To form giant planets during protoplanetary disk lifetime, small micron sized particles must grow rapidly to larger grains. A full understanding of that process requires a detailed characterization of the radial and vertical structure of the gas-rich disks associated with young pre-main sequence stars. Multi-wavelengths observations of protoplanetary disks, for example in the millimeter and near-infrared, allow to probe two widely separated grain sizes that are differently affected by evolutionary mechanisms such as radial drift and vertical settling. In this talk, I will present constraints on both mechanisms using multi wavelengths observations, with a longer focus on disks seen edge-on. Highly inclined disks are of particular interest because they provide a unique point of view to unambiguously disentangle their vertical and radial dimensions. The modeling of multi-wavelength observations of such disks allows to identify high density regions, favorable for grain growth and planet formation, and to study the efficiency of planet formation in protoplanetary disks.

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JWST’s First Stares at Transiting Exoplanet System

september 19, 2022   |   12 pm noon (MST)   |   Hybrid (SO 305 & Zoom)
everett schlawin,   steward observatory, u arizona
ABSTRACT

JWST is now peering into the atmospheres of planets and providing new insights about their composition with its unprecedented precision and window into the near-infrared and mid infrared. I will discuss our very first looks at the Universe from NASA’s premier space observatory, our initial performance tests as they relate to transiting planet science, what we learned about photometric stability from JWST’s first lightcurves of a transiting planet (HAT-P-14 b) and the systematic errors to look out for. I also will also share the first robust unambiguous detection of carbon dioxide in an exoplanet atmosphere (WASP-39 b) as part of a community Early Release Science program.

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“Adding Insult to Injury” – The discovery of the Nadir impact crater

september 26, 2022   |   12 pm noon (MST)   |   Hybrid (LPL room 330 & Zoom)
 veronica bray,   LPL, U Arizona
ABSTRACT

Evidence of marine target impacts, binary impact craters, or impact clusters are rare on Earth. Seismic reflection data from the Guinea Plateau, West Africa, reveal a ≥8.5-km-wide structure buried below ~300 to 400 m of Paleogene sediment with characteristics consistent with a complex impact crater. These include an elevated rim above a terraced crater floor, a pronounced central uplift, and extensive subsurface deformation. Numerical simulations of crater formation indicate a marine target (~800-m water depth) impact of a ≥400-m asteroid, resulting in a train of large tsunami waves and the potential release of substantial quantities of greenhouse gases from shallow buried black shale deposits. Our stratigraphic framework suggests that the crater formed at or near the Cretaceous-Paleogene boundary (~66 million years ago), approximately the same age as the Chicxulub impact crater. We hypothesize that this formed as part of a closely timed impact cluster or by breakup of a common parent asteroid.

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The Gaia and Extreme AO Revolution: Discovering, Weighing, and Characterizing Exoplanets and Brown Dwarfs

october 3, 2022   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Timothy brandt,   UC Santa barbara
ABSTRACT

While thousands of exoplanets and brown dwarfs are known, the theoretical models that allow us to interpret their spectra and luminosities are anchored by just a few with independently measured masses, ages (from their host stars), and atmospheric properties (inferred from spectra). I will present a combination of three observational techniques–astrometry, radial velocity, and imaging–to discover, weigh, and characterize massive exoplanets and brown dwarfs. Advances in adaptive optics and infrared instrumentation now enable us to see young exoplanets millions of times fainter than their host stars. Despite huge gains in sensitivity, however, high-contrast imaging surveys remain plagued by a lack of discoveries. I have calibrated a huge data set of stellar reflex motions; it can identify unseen planets and brown dwarfs by the gravitational tugs they exert on their host stars, and enable us to measure their masses and orbits. We have already begun to discover and weigh new substellar companions by targeting accelerating stars. With masses, orbits, and spectra of a growing sample of planets and brown dwarfs, we can finally test models of substellar formation and evolution.

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Complex Organic Molecules in the ISM: Methanol, Fullerenes, and Carbon Nanotubes

october 10, 2022   |   12 pm noon (MST)  |   Hybrid (LPL 309 & Zoom)
 jacob bernal 
alien earths team,  LPL, U Arizona
ABSTRACT

The detection of Complex Organic Molecules (COMs) such as methanol and the fullerenes C60 /C70 in the interstellar medium (ISM) has transformed our understanding of chemistry in space, and have also raised the possibility for the presence of even larger molecules in astrophysical environments. In this talk I will highlight the recent mm-wave detection of methanol in cold molecular clouds at the edge of the Milky Way Galaxy. I will also discuss in situ heating of analog silicon carbide (SiC) presolar grains using transmission electron microscopy (TEM), designed to simulate shocks occurring in post-AGB stellar envelopes. These experimental findings reveal that heating the analog SiC grains yields C60-sized nanostructures, which later transform into multi-walled carbon nanotubes (MWCNTs). These MWCNTs are larger than any of the currently observed interstellar fullerene species, both in overall size and number of C atoms. The implications for both these findings on the interstellar chemical scenario will be discussed.

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From the galactic to atomic scale: understanding planet formation and evolution 

october 17, 2022   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
 akash gupta,   uCLA
ABSTRACT
One of the most profound findings from NASA’s Kepler mission is the unexpected dearth of close-in exoplanets of sizes 1.5 to 2.0 Earth radii, i.e., a radius valley. This valley divides the population of the most abundant class of planets yet known, those between the sizes of Earth and Neptune, into small planets with Earth-like compositions and large planets with hydrogen-rich atmospheres or ice-rich interiors. Recently, we demonstrated that atmospheric mass-loss driven by the cooling luminosity of a planet and its host star’s bolometric luminosity can explain this observation, even in the absence of any other process. In this talk, I will describe the key physical processes that drive this core-powered mass-loss mechanism. I will present how our results compare with observations, the insights they give us and the testable predictions we make as a function of planet and host-star properties. This will include sharing our latest work on the characteristics of the radius valley around M dwarfs.

 

One of our significant findings is that most observed exoplanets have hydrogen atmospheres interacting with molten or super-critical interiors for millions to billions of years. In our Solar system, we see this for planets such as Jupiter and Neptune. Studies show that such interactions can have far-reaching implications for an atmosphere’s composition, structure, and evolution. However, we hardly understand these interactions, and studying them in a laboratory is difficult. I will discuss how we address this problem using quantum mechanical molecular dynamics. Specifically, I will share the findings of our upcoming work on the solubility of a planet’s hydrogen atmosphere in its super-critical water interior and their implications for planets and exoplanets such as Neptune.

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TITLE: The ALMA-IMF Large Program: SiO Gas at Low and High Velocities, and First Results from CMF Analyses

october 24, 2022   |   12 pm noon  (mst) |   Hybrid (lpl 309 & Zoom)
 allison towner,   University of florida
ABSTRACT
The ALMA-IMF Large Program seeks to understand the origins of the stellar IMF by studying the distribution of masses of pre- and protostellar cores (the Core Mass Function, or CMF) in 15 high-mass star-forming regions (protoclusters) in the Milky Way. The origin of the stellar IMF at the high-mass end remains a matter of some debate, with some studies suggesting that high-mass cores mirror the Salpeter slope and others suggesting that the CMF is top-heavy compared to the IMF. In this talk, I will present first results from CMF studies of protoclusters in the ALMA-IMF sample, including how the CMF may vary with a protocluster’s evolutionary state or even vary locally within a single protocluster. I will also discuss a census of the SiO gas in the full sample, including 1) our full catalog of 319 protostellar outflow candidates, the outflow properties, and their connections to global properties within each protocluster, and 2) low-velocity, narrow, non-asymmetric SiO emission which is ubiquitous in our sample and may trace relic shocks or purely low-velocity processes. I will also discuss how these two types of emission relate to the overall evolutionary state of each protocluster.

 

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Characterizing 3D Magnetic Fields in star-forming regions

october 31, 2022   |   12 pm noon (MST)  |   Hybrid (SO N305 & Zoom)
 yue hu,   universitiy of wisconsin-madison
ABSTRACT

Magnetic field, turbulence, and self-gravity are important in understanding star formation. However, 3D magnetic field orientation and strength were barely accessed. Based on our recently understanding of dust polarization and anisotropic MHD turbulence, I will present two novel methods, i.e., polarization fraction analysis (PFA) and velocity gradient technique (VGT), in tracing the 3D magnetic field orientation. By combing with the Davis–Chandrasekhar-Fermi method or the Differential Measure Analysis, I will show that the 3D magnetic field distribution, including both orientation and strength, is successfully recovered in the low-mass star-forming region L1688. The second method VGT employs spectroscopic emission lines to derive the magnetic field. I will show that VGT-measurement advantageously gets rid of the contribution from the cloud’s foreground/background. By using multiple molecular tracers, VGT reveals the magnetic field’s variation in different volume density regimes. I will discuss gravitational collapse’s effects on velocity gradient and briefly present VGT’s application of tracing magnetic fields in nearby galaxies.

 

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(small) ground-based telescopes are crucial for spaced-based observatories

november 7, 2022   |   12 pm noon  (MST) = 11 Am PST  |   Hybrid (LPL 309 & Zoom)

NOTE: TIME CHANGE 

 robert zellem, JPL
ABSTRACT

Due to the efforts by numerous ground-based surveys and NASA’s Kepler and Transiting Exoplanet Survey Satellite (TESS), there will be hundreds, if not thousands, of transiting exoplanets ideal for atmospheric characterization via spectroscopy with large platforms such as James Webb Space Telescope and ARIEL. However their next predicted mid-transit time could become so increasingly uncertain over time that significant overhead would be required to ensure the detection of the entire transit. As a result, follow-up observations to characterize these exoplanetary atmospheres would require less-efficient use of an observatory’s time—which is an issue for large platforms where minimizing observing overheads is a necessity. Here we demonstrate the power of citizen scientists operating smaller observatories (~1 m) to keep ephemerides “fresh,” defined here as when the 1σ uncertainty in the mid-transit time is less than half the transit duration. Here we describe Exoplanet Watch, a community-wide effort to perform ephemeris maintenance on transiting exoplanets by citizen scientists. Such observations can be conducted with even a 6 inch telescope, which has the potential to save up to ∼10,000 days for a 1000-planet survey.

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MIRAC-5 and METIS: near and long-term prospects of ground-based MID-IR Astronomy

november 8, 2022 (TUESDAY)   |   12 pm MST = 11AM PST  |   Hybrid (SO N305 & Zoom)
 Rory bowens, university of michigan
ABSTRACT

Mid-infrared astronomy is a critical wavelength regime for the study of targets from planets to galaxies. Paired with direct imaging, we can unveil knowledge of planet luminosities, temperatures, and atmospheric compositions. In this talk, I will discuss near and long-term advancements in the field of ground-based mid-IR imaging. First, I will present the fifth incarnation of the Mid-Infrared Array Camera (MIRAC-5) instrument which will use a new GeoSnap (3 – 13 microns) detector. As one of the only 3 – 13 micron cameras used in tandem with adaptive optics (AO), MIRAC-5 will be complementary to the James Webb Space Telescope (JWST) and capable of characterizing gas giant exoplanets and imaging forming protoplanets (helping to characterize their circumplanetary disks). I will describe key features of the MIRAC-5 GeoSnap detector and summarize MIRAC-5’s important science capabilities, including prospects for obtaining the first continuum mid-infrared measurements for several gas giants and the first 10.2-10.8 micron NH3 detection in the atmosphere of the warm companion GJ 504b (Teff ~ 550 K) within 8 hours of observing time. MIRAC-5 will be commissioned on the MMT utilizing the new MAPS AO system in 2023. I will then discuss long-term plans for mid-IR direct imaging in the era of 30 m class telescopes which will have the angular resolution and sensitivity to directly image planets with R < 4 R⊕ around the very nearest stars. I predict yields from a direct imaging survey of a volume-limited sample of Sun-like stars with the Mid-Infrared ELT Imager and Spectrograph (METIS) instrument, planned for the 39 m European Southern Observatory Extremely Large Telescope (ELT). Using Kepler occurrence rates, a sample of stars with spectral types A-K within 6.5 pc, and simulated contrast curves based on an advanced model of what is achievable from coronagraphic imaging with adaptive optics, I estimate the expected yield from METIS using Monte Carlo simulations. I find the METIS expected yield of planets in the N2 band (10.10−12.40 μm) is 1.14 planets and also determined a 24.6% chance of detecting at least one Jovian planet in the background limited regime assuming a 1 h integration. I will conclude with an observing strategy aimed to maximize the possible yield for limited telescope time, resulting in 1.48 expected planets in the N2 band.

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revealing Atmospheric Trends on Irradiated Brown Dwarfs with Phase-resolved HST/WFC3 Spectroscopy

november 14, 2022   |   12 pm noon  (MST) |   Hybrid (SO N305 & Zoom)
 rachael amaro,  
alien earths team, steward observatory, u arizona
ABSTRACT
Brown dwarfs in tidally-locked orbits around white dwarfs offer an exciting opportunity to explore properties of irradiated atmospheres. These highly irradiated brown dwarfs have ultrashort rotation periods (<2 hours), weak to strong internal heat flux, and intense external irradiation, making them an ideal testbed for investigating the importance of these parameters on key atmospheric processes. In this talk, we will present high-quality, phase-resolved HST/WFC3 spectroscopy from 1.1 to 1.7 microns of the binary system NLTT5306, a ~1700 K brown dwarf in a ~102 minute orbit around a white dwarf. With this brown dwarf, our team addressed two key questions driving atmospheric studies: (1) understanding the structure and formation/disruption of clouds under the presence of intense, tidally-locked irradiation, and (2) characterizing the efficiency of day-to-night heat redistribution. Finally, we end with an overview of the constraints on cloud cover and atmospheric dynamics in four irradiated brown dwarfs, exploring trends with irradiation level, temperature, and rotation period.

 

Complex organic molecules around low- and high-mass protostars

november 21, 2022   |   12 pm noon (MST)   |   Hybrid (lpl 309 & Zoom)
Pooneh Nazari,   leiden observatory
ABSTRACT

Planet cores are thought to start forming around protostars where many complex organic molecules are detected. Therefore, understanding the chemistry of these species helps us understand the chemistry of the forming planets. There are already high-sensitivity studies of complex chemistry toward single sources. However, a high-sensitivity statistical analysis of complex organics toward low- and high-mass protostars is missing. I will show results from observations of these species around ~40 high-mass protostars. Moreover, I will discuss how physical conditions can affect the observations of complex organics and our interpretation of the chemistry using radiative transfer models.

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Inheritance of the Sun’s Short-Lived Radionuclides and Statistical Chronometry

november 28, 2022   |   12 pm noon  (MST) |   Hybrid (SO N305 & Zoom)
 steve desch,   arizona state university
ABSTRACT
At the Origins Seminar in April, Sasha Krot and I debated the origins of the short-lived radionuclides (SLRs) like 26Al and 10Be in the early Solar System. I argued that they were almost entirely inherited from the Sun’s molecular cloud. One line of evidence was the uniformity of 10Be/9Be ratios in all the calcium-rich, aluminum-rich inclusions (CAIs) that faithfully record the value they formed with in the solar nebula; this precludes irradiation in the disk as a significant source of SLRs (except for 36Cl). Another line of evidence was the low value 60Fe/56Fe ~ 10^-8 in all meteoritic samples, which obviates the need for late injection from supernovas as a source of SLRs. A third line of evidence was the concordance of ages derived using Pb-Pb, Al-Mg, Mn-Cr, and Hf-W chronometry, which implies uniformity of the SLRs 26Al, 53Mn, and 182Hf in the solar nebula. In this talk I will expand on this third line of evidence.
We have developed a mathematical framework we call “statistical chronometry” that allows us to find the optimal values of four parameters—(53Mn/55Mn)SS, (182Hf/180Hf)SS, the 53Mn half-life, and the Pb-Pb age of t=0—that maximize the concordance of the different radiometric dating systems, assuming the SLRs were uniformly distributed. We show that the rapidly cooled achondrites that must be concordant, are indeed concordant, strongly suggesting homogeneity of the SLRs. The Pb-Pb age of t=0 is 4568.6 Myr, 1.4 Myr older than is commonly reported for CAIs; we demonstrate that it is likely that the U-Pb system was disturbed in CAIs after they formed. There remains some evidence for 26Al heterogeneity in certain rare, small inclusions; but we show that these are all dominated by corundum or hibonite, indicating a chemical heterogeneity, not a spatial or temporal one. We discuss how this might have occurred. The picture that emerges is that the Sun formed in a spiral arm in the Galaxy, in a region with high star-formation rate, and inherited almost all of its SLRs from the molecular cloud, contaminated by supernovas but especially Wolf-Rayet stars.
Many of these ideas are also explored in the upcoming book chapter by Desch, Young, Dunham, Fujimoto & Dunlap for the Protostars and Planets VII conference:  https://arxiv.org/abs/2203.11169

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Rotational evolution of young stars

december 5, 2022   |   12 pm noon (MST)  |   Hybrid (lpl 309 & Zoom)
Marina Kounkel, Vanderbilt University
ABSTRACT

In the recent years, with advancements of large surveys such as Gaia and TESS, the ability to measure ages of stars has significantly improved. Current census of stars with know ages exceeds a million stars, and it may soon increase by an order of magnitude. Through measuring rotational periods of variable stars with known ages, we develop an empirical gyrochronology relation of angular momentum evolution that is valid for slowly stars with ages up to 1 Gyr, with the typical precision of ~0.2-0.3 dex. Rapid rotators on the other hand appear to be associated with binary systems with intermediate range of separations, having been sped up following their loss of protoplanetary disks. These data enable detailed characterization of the early evolution of the fundamental properties of stars, and also reveal biases in our observations of the youngest stars.

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The mysteries of gaps and pile-ups at planetary resonances

december 12, 2022   |   12 pm noon (MST)   |   Hybrid (SO N305 & Zoom)
Renu Malhotra,  
alien earths team, lpl, U Arizona
ABSTRACT

The orbital spacings of planets, the locations of planetesimal belts, the dynamical transport of planetary impactors, and the long term stability of planetary systems are all mostly controlled by orbital resonances. Orbital resonances also have practical applications, such as estimating exo-planet masses and designing low-thrust spacecraft trajectories. But orbital resonances are paradoxical, presenting the potential for enhanced stability as well as enhanced instability. In this pre-holiday edition of the Origins seminar I will attempt to explain some of the mysteries of gaps and pile-ups that are observed at planetary resonances.

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Summer 2022

planet formation across different stellar evolutions

august 1, 2022   |   12 pm noon   |   Hybrid (SO N305 & Zoom)
Nicolas Kurtovic, MPIA Heidelberg
ABSTRACT

Planet formation seems to be ubiquitous around young stellar objects. In this talk I will explore the conditions for planet formation across different stellar masses, disk ages, and stellar multiplicity, through the scope of ALMA observations. My work focuses on describing the finest details in the disks emission, to obtain insight into how their future planetary architectures will look like. More about my work in www.nicolaskurtovic.com. 

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Spring 2022

The architectures of planetary systems: population synthesis meets observations

january 24, 2022   |   12 pm noon   |   Zoom

Martin schlecker, steward observatory, University of arizona
ABSTRACT

Exoplanets are now routinely detected and their properties, such as their mass and orbital periods, can be constrained to high precision. While it is widely recognized that multiple planets per system are common, their mutual relationships are still largely unexplored. By confronting simulated planet populations with observed exoplanets, I will show that planetary properties and the architectures of their host planetary systems are related, and, more specifically, that observables of small planets on short orbits might be used to infer the existence of additional planetary companions. I will discuss how a solidification of this prediction has the power to constrain central open questions in contemporary planet formation theory, ranging from the efficiency of pebble accretion to planet migration.

 

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Contextualising Planetary Systems Through Galactic Archaeology Surveys

 

january 31, 2022   |   12 pm noon   |   Zoom
jake clark, Fulbright Future Scholar, University of Southern Queensland
ABSTRACT

There is an ever growing abundance of stellar surveys exploring the formation and evolution of our galaxy. These surveys collect and derive the properties for 100,000s of stars, which can also be used to better understand the properties of planet-hosts across the Milky Way.

My talk will showcase how valuable such surveys can be to the exoplanet community through my dissertation work using the galactic archaeology survey known as GALAH. I have been able to use GALAH, along with other surveys to better characterise both the chemical and physical properties of stars observed by the TESS mission. This has led to learning more about the stellar populations of planet-hosts across the Galaxy to uncovering clues towards the formation mechanisms of ultra-short period planets. I will also show how my work is useful for exogeologists in calculating the potential compositions of newly found worlds, to better understand their potential habitability.

 

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Alien Earths: The Search for Habitable Worlds around Nearby Stars

february 7, 2022   |   12 pm noon   |   Zoom
dániel apai, university of arizona (Steward observatory and  LPL, University of Arizona)
ABSTRACT
With the number of extrasolar planet discoveries increasing rapidly, a key emerging frontier of exoplanet research is the search for potentially habitable planets around nearby stars. It is these relatively nearby planets that we may hope to survey in the near future for potential atmospheric signatures of life. However, due to the challenging nature of exoplanet observations, the majority of nearby planets remain undiscovered. In addition, the nature of many known, nearby planets remains still poorly understood due to the lack of data on their fundamental properties.
In this talk, I will present our large, NASA ICAR interdisciplinary project Alien Earths which aims to address these challenges. Our Alien Earths team works toward developing a comprehensive, integrative framework to study and characterize nearby planetary systems to determine which of them are more likely to harbor habitable worlds. In this talk, I will also show examples of how the architectures and the presence of planets in nearby planetary systems can be successfully predicted by combining system-specific but incomplete information with robust, population-level, statistical constraints. I will also describe how Alien Earths combines multiple lines of evidence to characterize nearby planetary systems and support target selection and the interpretation of observations of future missions that search for life on other worlds.

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Water planet thresholds: The topographic scope for land atop a stagnant lid

february 14, 2022   |   12 pm noon   |   Zoom
Claire Guimond, University  of Cambridge, Dept. of Earth Science
ABSTRACT

Small water budgets produce desert worlds and large ones produce water worlds, but there is a narrow range of water budgets that would grant a marbled surface to a rocky planet. A planet’s topography can delimit this range in that it controls how much water could rest on the surface before flooding it. Thus we take a step in quantifying water world limits by estimating how minimum surface elevation differences scale with planetary bulk properties. Our model does not require the presence of plate tectonics, an assumption which has constricted the scope of previous studies on exoplanet land fractions. We focus on the amplitudes of dynamic topography created by rising and sinking mantle plumes—obtained directly from models of mantle convection—but also explore rough limits to topography by other means. Rocky planets several times more massive than Earth can support much less topographic variation due to their stronger surface gravity and hotter interiors; these planets’ increased surface area is not enough to make up for low topography, so ocean basin capacities decrease with mass. In cooler thermal states, dynamically-supported topography alone could maintain subaerial land on Earth-size stagnant lid planets with surface water inventories of up to approximately 100 ppm of their mass (or half Earth’s ocean mass fraction). Considering the overall cap to topography on such planets would probably raise this threshold ocean mass fraction by an order of magnitude.

 

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Molten exoplanets as a window into the earliest Earth

february 21, 2022   |   12 pm noon   |   Zoom

Tim Lichtenberg, university of oxford (Alien earths team)
ABSTRACT

Due to the absence of a reliable rock record from the Hadean eon, our understanding of the planetary environment that gave rise to life on the earliest Earth is clouded. Upcoming exoplanet surveys, however, will significantly expand our view of the distribution and variability of rocky planets and their chemical inventories, giving opportunity to test scenarios of early planetary evolution. I will describe recent efforts to establish a comprehensive theoretical framework to simulate the coupled evolution of solidifying planetary mantles and their outgassing atmospheres on young rocky worlds for a wide range of instellation, mass, and composition. The presence or absence of magma oceans on short-period exoplanets can alter the observationally inferred bulk water abundance by up to one order of magnitude, motivating reassessments of previous escape studies including volatile locking in the planetary interior. Alternating cooling trajectories during primary envelope loss on sub-Neptunes can quench metal core formation and thus induce a qualitative change in mantle redox state, which alters the expected compositions of secondary atmospheres on super-Earths. Both of these effects are within the currently observationally accessible limits for individual exoplanetary systems and will be statistically testable with next-generation transit surveys. Increasing reconnaissance of high-temperature super-Earths will enable us to infer the early climatic and geodynamic evolution of temperate rocky worlds, and thus provide crucial information on the environmental context of the origins of life on Earth.

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TITLE: The Roaring 20s: The Coming Revolution in Exoplanet Atmospheres

february 28, 2022   |   12 pm noon   |   Zoom

Thomas Beatty, steward observatory, university of arizona
ABSTRACT

It is now clear that exoplanets are ubiquitous in the galaxy. Though our understanding of exoplanet demographics has dramatically expanded over the last quarter-century, many fundamental questions about their origins and physical properties remain. For example, we lack a complete understanding of the chemical and physical processes shaping exoplanet atmospheres, including a full description of their clouds, the abundances of specific species, and the role of disequilibrium chemistry. We also do not well understand what makes a terrestrial planet habitable, with conditions conducive to life, rather than a dead planet. The atmospheric characterization of exoplanets plays a key role in helping us answer these questions, and with successful launch of JWST and the construction of new ground-based facilities, we are poised at the start of a new era of exoplanet observations. I will discuss what atmospheric characterization observations have shown us, and what we can expect to see in the next few years, about planet formation pathways and evaluating the potential habitability of exoplanets.

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TITLE: Providing new constraints on the surface composition of Europa

march 14, 2022   |   12 pm noon   |   Zoom

 Ishan Mishra, cornell university
ABSTRACT

Composition of Europa’s surface remains our best window into the composition of its subsurface ocean, and spectroscopy is our primary tool for characterizing its surface’s composition. Of special interest are trace species like organics and oxides, whose presence and abundance distributions can provide valuable insights into the potential habitability of the subsurface ocean. I will present a data analysis framework for reflectance data, based in Bayesian statistics, that specializes in picking out trace signals in spectroscopic data. This Bayesian framework can quantify confidence in the presence of a given species, constrain its parameters like abundance and average grain size with confidence intervals, and explore solution degeneracies. I will show examples of its application to Europan data from Juno and Galileo missions in my recently published works. I will also talk about my current project of using this framework to assess the feasibility of detection and characterization of organics on Europa with current and upcoming instruments

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TITLE: the ancient solar system revealed by lkunar exploration and impact cratering

march 21, 2022   |   12 pm noon   |   Zoom

 Sam Cabot, yale university
ABSTRACT

Imminent Lunar exploration missions will provide opportunities to analyze the Moon’s regolith and resolve fundamental questions about the ancient Solar System. We discuss specific examples of ancient impact cratering processes that may have their signatures preserved in the Lunar regolith. First, we demonstrate that if Venus’ atmosphere was at any point thin and similar to Earth’s, then asteroid impacts transferred detectable amounts of lightly-shocked, Venusian surface material to the Moon’s surface. These rocks are well-preserved on the Moon, which lacks an atmosphere and significant geological activity. An ancient Venusian rock could constrain Venus’ history, and reveal the past existence of oceans. Second, we discuss how impact cratering may reveal the compositions and dynamical histories of Interstellar Objects (ISOs). At present, no theory satisfies both observational constraints and physical limitations imposed by formation processes. We show that impacts on Kuiper Belt analogues do not generate the sufficient quantity of large, nitrogen ice fragments necessary to explain ‘Oumuamua’s detection. We gauge the feasibility of identifying Lunar craters formed by anomalously fast (100 km/s) ISO impacts. While such craters should be extremely rare, melt volume and high-pressure petrology in Lunar craters may be diagnostic features once large volumes of material can be analyzed in situ. 

TITLE: A Hydrodynamic study of the escape of metal species and excited hydrogen in the atmosphere of the hot jupiter WASP-121B 

march 28, 2022   |   12 pm noon   | hybrid (zoom + SO N305)

Chenliang Huang, LPL, University of Arizona

ABSTRACT

Imminent The heating by photoionization in the thermosphere of short-period exoplanets can drive hydrodynamic escape, which is key to understanding the evolution of planetary atmospheres and explaining transit observations.  Besides powering atmospheric escape, the energy deposited by extreme UV photons from the host star can also be radiated away through collisionally excited atomic spectral lines.  In addition, metals and excited-state hydrogen, which have lower ionization potentials than 13.6 eV, can absorb the longer wavelength photons in the stellar spectrum.  These two factors, in addition to Roche lobe overflow, can cause the mass loss rate to exceed the traditional energy-limited value.  In the near UV and optical transmission spectrum of the hot Jupiter WASP-121b, recent observations have detected strong absorption features of Mg, Fe, Ca, and Hα, extending outside the planet’s Roche lobe.  Studying these atomic signatures can directly trace the escaping atmosphere and constrain the thermal processes in the upper atmosphere. To understand these features, we construct a sophisticated forward model by expanding the capability of the exoplanet hydrodynamic atmosphere code introduced in Koskinen et al. 2013, to include important processes of atomic metal species and excited hydrogen.  Using this model, we can reproduce and interpret detected atomic features in the transmission spectrum of WASP-121b self-consistently.

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TITLE: Peering at Hazy Worlds Near and Far Through Laboratory Experiments

april 4, 2022   |   12 pm noon   |   hybrid (zoom + SO N305)

sarah moran, university of arizona (LPL)
ABSTRACT

Photochemical hazes are found across the Solar System and in exoplanetary atmospheres, with important effects on atmospheric chemistry and subsequent possible impacts on observations. These affect current observations from Hubble, future observations from JWST, as well as potential upcoming planetary missions. I will present results of the composition of haze particles produced from exoplanet and Triton laboratory studies in the JHU PHAZER laboratory. With high resolution mass spectrometry, we detected many complex molecular species in the haze particles, including those with prebiotic applications. We also measured the haze particles’ spectra with visible-infrared spectroscopy. Our experimental exoplanetary haze analogues exhibit diverse physical properties, which may help us understand their role as potential cloud condensation nuclei and their role in subsequent atmospheric evolution. The Triton experiments reveal the unexpected role of carbon monoxide and its effect on haze formation in Triton’s atmosphere and beyond. Finally, I will discuss how we can apply what we’ve learned from the laboratory into atmospheric models for existing and future observations of sub-Neptune-sized exoplanets as well as Neptune’s moon, Triton.

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Towards Quantifying Habitability: Progress Update from the NExSS QuantHabitability Science Working Group

april 11, 2022   |   12 pm noon   |   Zoom

Dániel Apai, University of Arizona, NExSS/Alien Earths Team
ABSTRACT
Exoplanet habitability plays a central role in the future of exoplanet exploration and the science cases for ambitious ground- and space-based telescopes. As habitability depends on many factors – some of which are observable, while others are not – establishing the likelihood of a given’s planet habitability based on remote sensing data remains challenging. At the same time, there is an increasing urgency for a self-consistent framework that provides a quantitative approach to habitability, to inform trades and strategies for possible future mission concepts. The NASA Nexus for Exoplanet System Science (NExSS) Research Coordination Network launched a science working group to integrate community input and work toward developing a quantitative framework for habitability. In this talk, I will present an overview of the QuantHab SWG’s work and review its plans for the next year. Following the presentation, we will discuss the context and challenges of assessing habitability and considerations for a quantitative framework.

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Exploring the chemical diversity of sub-Neptune planets

april 18, 2022   |   12 pm noon   |   Zoom

andrea guzman mesa, University of bern

 

ABSTRACT
The atmospheres of sub-Neptunes are expected to exhibit considerable chemical diversity, beyond what is anticipated for gas-giant exoplanets. In my talk, we explore self-consistent atmosphere-interior models of sub-Neptunes to explore this chemical diversity and apply this knowledge to the available atmospheric data of GJ 436b and link it with the corresponding plausible internal structures a presented in Guzmán-Mesa et al 2022. 

 

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DEBATE: WHAT DO SHORT-LIVED RADIONUCLIDES TELL US ABOUT THE BIRTH OF THE SUN?

april 25, 2022   |   12 pm noon   |   Zoom

Steve Desch (ASU) & Sasha krot (univ of hawaii)

ABSTRACT

Meteoritic data is an exquisite tool for probing the conditions and events surrounding the early Solar System. An especially important clue to the Sun’s astronomical birth environment is the inference from meteorites that a dozen or more short-lived radionuclides (SLRs), with half-lives ~0.1-10 Myr, existed in the early Solar System. The discovery (Lee et al. 1976) of 26Al in the solar nebula immediately spawned theories (Cameron & Truran 1977) that the Sun had to have formed near a supernova. That image, though inaccurate, remains embedded in astronomers’ minds. But how should we interpret the meteoritic data?

Astrophysical models for the Sun’s formation today tend to fall into three camps. In “inheritance” models, the SLRs were all inherited from the Sun’s molecular cloud, which was likely enriched in SLRs by multiple generations of ‘nearby’ massive stars (supernovae, and especially Wolf-Rayet winds). In “injection” models, at least some SLRs were injected late into the collapsing molecular cloud, or even protoplanetary disk, by a single massive star (supernova or Wolf-Rayet wind). In “irradiation” models, at least some SLRs were created in the protoplanetary disk, by nuclear reactions involving Solar Energetic Particles.  

These models predict different outcomes for the SLRs in meteorites. In “inheritance” models, all SLRs were present from the earliest times in the solar nebula, and spatially uniform. The abundances of SLRs in meteoritic components should reflect their time of formation. In “injection” models, temporal and possibly spatial heterogeneities in injected SLRs are predicted, with some isotopes (26Al and 60Fe) present before the injection but absent before. High abundances of 60Fe would demand such models.  In “irradiation” models, SLR abundances, especially that of 10Be, should be higher near the Sun and likely decrease in time. 

Determining which model(s) applies to the Solar System depends on answer three questions about three key SLRs in meteorites:

  1. What was the level of 60Fe (t1/2 = 2.6 Myr) in the early Solar System?  If closer to 60Fe/56Fe ~ 10-6, this would imply injection from a nearby supernova. A level closer to 60Fe/56Fe ~ 10-8, would be consistent with inheritance. 
  2. Was 26Al (t1/2 = 0.7 Myr) homogeneously distributed across time and space in the solar nebula? The existence of meteoritic components with very low 26Al/27Al, and/or big variations in different reservoirs, would appear more consistent with injection. 
  3. Was 10Be (t1/2 = 1.4 Myr) homogeneously distributed across time and space in the solar nebula? Variations would imply an important role for irradiation. 

 

Renowned meteoriticist Sasha Krot (U. Hawaii) and (mostly) astrophysicist Steve Desch (Arizona State) will offer different perspectives on the current answers to these questions.

Steve’s starting position is that the SLRs are overwhelmingly attributable to inheritance from the molecular cloud, with a very limited role for irradiation in the solar nebula, and essentially no role for injection. Previous inferences of a high abundance 60Fe/56Fe~10-6 were incorrect, and more recent inferences of 60Fe/56Fe~10-8 are correct. He would characterize the meteoritic components with low 26Al/27Al as being rare and in other ways atypical. The 10Be/9Be ratios in meteoritic components are not just predominantly uniform, but entirely consistent with a single homogeneous value, despite claims made about few inclusions. Steve would say the abundances of SLRs in the molecular cloud were set by a combination of Galactic Chemical Evolution plus self-enrichment by generations of previous massive stars in the same spiral arm, especially by Wolf-Rayet winds. The SLR abundances in different meteoritic components tend to comply with a single, consistent chronology. 

Sasha’s starting position is that SLRs may be mostly determined by inheritance, but that the molecular cloud had spatial and temporal variations of SLRs due to injection of material into it, translating into heterogeneities in the disk. He also would agree that inferences of 60Fe/56Fe ~ 10-8 are correct, making a Wolf-Rayet wind more likely than a supernova to be injecting material. But Sasha is more likely than Steve to interpret the refractory Ca,Al-rich inclusions (CAIs) lacking 26Al to be widespread (e.g., >85% of CH CAIs), reflecting a true temporal (or spatial) heterogeneity in the disk. Likewise, Sasha attaches more significance to the findings of heterogeneous 10Be/9Be in CAIs. Sasha therefore sees a potentially significant role for injection and irradiation in the solar nebula. 

Steve and Sasha may or may not come to an agreement on these issues, but the hope is that the audience walks away with a greater appreciation of the state of the field: what are the likely astrophysical models; how is meteoritic data collected and what are the current interpretations; and especially, what research in the near term could settle the debates! 

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understanding the carbon inventory pf terrestrial planets: earth’s depletion and implications for habitable planets

may 2, 2022   |   12 pm noon   |  hybrid (zoom + SO N305)

fred ciesla (Alien earths team, University of Chicago)
ABSTRACT

The bulk composition of a planet, and the accessibility of key molecules and elements at its surface will be critical in determining whether a biosphere can develop and be maintained.  Water has long been recognized as an important ingredient for the formation and maintenance of life, and thus is the basis for defining the Habitable Zone for planets around a star.  However, life requires access to many other molecules and elements, and their abundances must also be factored in when determining whether a planet may be suitable for life.  The Bulk Silicate Earth (BSE) exhibits a clear elemental depletion trend, with the abundance an element decreasing with decreasing condensation temperature.  This holds for carbon, whose abundance is very low in the BSE.  In this talk, I’ll review Earth’s carbon deficit and discuss the processes that may have operated during planet formation to define it.  I will then discuss what this may mean for carbon inventories of other planets, particularly terrestrial planets which formed in the Habitable Zones of their host stars.  

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Observational constraints on the chemical complexity and evolution of low mass starless and prestellar core

may 9, 2022   |   12 pm noon   |   hybrid (zoom + SO N305)

samantha Scibelli
steward observatory, University of arizona

ABSTRACT: 

Before a low-mass (M ≤ few solar masses) star like our Sun is formed, it is conceived inside a cold (~10 K) and dense (> 105 cm-3) region of gas and dust known as starless or dynamically evolved prestellar core. It is essential to study the chemical complexity and evolution of prestellar cores because they set the initial conditions of star and planet formation. Observations of complex organic molecules (COMs) in prestellar cores has sparked interest in the star formation community due to the astrochemical and astrobiological implications. I will discuss my observations and abundance measurements of COMs in prestellar and starless cores in the Taurus Molecular Cloud, the prevalence of which support the idea that some COMs are seeded early on before the formation of protostars and planets. I also will discuss my recent modeling efforts to pinpoint the exact evolutionary states of a subset of these cores. Outside of Taurus, it is still unclear how abundance and evolutionary trends hold for prestellar cores in different environments. I will present early results from a new COM survey in the Perseus and Aquila molecular clouds that targets more than 50 starless cores. I stress that studying the limits of chemical complexity in prestellar cores is crucial for tracing how COMs are inherited from a cold core to a planetary system.

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A Bayesian, population level approach to constrain planet formation based on ALMA disk measurements

may 10, 2022 (special origins talk)   |   12 pm noon   |  hybrid (zoom + LPL309)

REmo burn, MPIA, heidelberg
 

ABSTRACT

A planet formation model can only be tested against observations if the initial properties of the protoplanetary disk are constrained. The most robust data is however obtained for evolved Class II objects with ages around 2 Myr. After a brief review of recent advances in population synthesis models, I focus on a Bayesian retrieval study of initial conditions and unknown parameters like the strength of viscous turbulence. We based the retrieval on observations of disks in young clusters on the ALMA continuum millimeter flux and accretion luminosity plane. As forward model, we use a neural net trained on 100’000 realizations of a viscous disk model including dust evolution and planetesimal formation. Within this framework, we find preliminary posterior distributions of key quantities describing the disks and can therefore constrain the stage for planet formation. Our Bayesian framework is well suited to produce distributions of parameters which can be used in future planet formation studies.

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The Long and Short of It: the Population of Earths, from Short Periods to the Habitable Zone

may 16, 2022   |   12 pm noon   |   Zoom

Galen bergsten (LPL, Universit of Arizona, Alien earths)
ABSTRACT

The search for the “next Earth” requires an understanding of the frequency and distribution of Earth-sized extrasolar planets in the habitable zones of Sun-like stars. Yet a lack of reliable detections for such planets has forced many estimates to be based on extrapolations from the population of planets much closer to their stars. However, these close-in planets might lose their atmospheres due to irradiation from their host stars, causing their distributions to evolve differently than those of planets in the habitable zone. In this talk, I will first discuss the population-level atmospheric evolution of small short-period planets, and consider how this relates to observations of the present-day planet population. I will then introduce a framework which shows how the evolved distribution of these planets is linked to the mass of their host stars, which may provide insights into the dominant mechanism(s) of atmospheric loss. I will also discuss how this characterization of shorter-period planets can be used to constrain the abundance of planets in the longer-period habitable zone, and consider how new estimates might impact future missions to detect and characterize Earth-sized habitable exoplanets.

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Fall 2021

Searching for an MHD Disk Wind Component via Optical Forbidden Emission Line Spectro-astrometry

August 23 , 2021   |   12 pm noon   |   Zoom
Emma Whelan, Maynooth University, Ireland

 

ABSTRACT

A crucial step in understanding how stars accrete their mass, as well as how disks evolve, is clarifying how the accreting disk gas loses angular momentum with both MHD disk winds and MRI induced turbulence explored. Recent simulations find that non-ideal MHD effects suppress MRI over a large range of disk radii, restoring radially extended MHD disk winds as the prime means for extracting angular momentum and enabling accretion at the observed rates. On the observational side, there has been renewed interest in identifying disk wind tracers and testing the emerging paradigm of disk evolution. Emission from optical forbidden lines has been a long-established tracer of flowing material from young stars with the low velocity component of emission region thought to trace the disk wind component of the flow. Here I report the results of a study which used spectro-astrometry to disentangle the origin of the [O I]6300 and [S II]6731 low velocity component in a sample of T Tauri stars. Particular goals were to understand if the low velocity narrow and broad components have different origins and to constrain the mass outflow to accretion rates in any wind component identified. 

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Rotating filament in Orion B – Do cores inherit their angular momentum from their parent filament?

August 30 , 2021   |   12 pm noon   |   HYBRID (Zoom+In person)
Cheng-Han HSIEH, Yale university

ABSTRACT

Angular momentum is one of the most important physical quantities that govern star formation. The initial angular momentum of cores may be responsible for its fragmentation and can influence the size of the protoplanetary disk. To understand how cores obtain their initial angular momentum, it is important to study the angular momentum of filaments where they form. While theoretical studies on filament rotation have been explored, there exist very few observational measurements of the specific angular momentum in star-forming filaments. Our high-resolution N2D+ ALMA observations of the LBS23 (HH24-HH26) region in Orion B shows a rotating filament with a total specific angular momentum (4 x10^20 cm^2s^-1). The dependence of the specific angular momentum with radius (j(r) \propto r^1.83) and the ratio of rotational energy to gravitational energy (\beta_{rot} ~ 0.04) are comparable to those observed in rotating cores with sizes similar to our filament width (~0.04 pc) in other star-forming regions. Our filament angular momentum profile is consistent with rotation acquired from ambient turbulence and with simulations that show filament and cores develop simultaneously due to multi-scale growth of nonlinear perturbation generated by turbulence.

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ALMA characterization of dust grain in Sz91 transitional disk

september 13 , 2021   |   12 pm noon   |   Zoom
Karina Maucó, Universidad de Valparaíso in Chile

ABSTRACT

One of the most important questions in the field of planet formation is how mm-cm sized dust particles overcome the radial drift and fragmentation barrier to form kilometer-sized planetesimals. ALMA observations of protoplanetary disks, in particular transition disks or disks with clear signs of substructures, can provide new constraints on theories of grain growth and planetesimal formation and therefore represent one possibility to progress on this issue. In this talk I will present high-angular resolution ALMA band 4 (2.1 mm) observations of the transition disk system Sz 91 and compare them with previously obtained band 6 (1.3 mm) and 7 (0.9 mm) observations. Sz 91 with its well-defined mm-ring, more extended gas disk, and evidence of smaller dust particles close to the star, is a clear case of dust filtering and the accumulation of mm-sized particles in a gas pressure bump. By performing a radial analysis of the multiband ALMA observations we derived a nearly constant spectral index through out the ring of 3.34, estimated the optical depth of the emission (marginally optically thick), and obtained maximum grain sizes in the sub-mm range (amax∼0.61 mm) in the dust ring. Comparing these results with recently published simulations of grain growth in disk substructures we found that our observational results are in very good agreement with the predictions of models for grain growth in dust rings that include fragmentation and planetesimal formation through the streaming instability.

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Why do small stars have all the exoplanets?

september 27 , 2021   |   12 pm noon   |   Zoom
Gijs mulders, Universidad Adolfo Ibáñez in Santiago de Chile

ABSTRACT

The demographics of exoplanets show that planet formation has to be a very efficient process, capable of forming planetary systems in a wide range of environments. One puzzling observation is the high occurrence of transiting planets around low-mass M dwarfs, where a reduced planet formation efficiency would be expected based on low protoplanetary disk masses.

In this talk I will paint a consistent picture of exoplanet populations — mainly consisting of hot sub-Neptunes and cold giant planets — that is constrained by transit, radial velocity, direct imaging, and micro-lensing surveys, and that is also compatible with observed protoplanetary disk structures.

To solve the M dwarf riddle, I will present a pebble accretion model where giant planet cores forming outside the snow line block the drift of pebbles into the inner disk, suppressing the formation of rocky planets there. This leads to a decreased occurrence rate of super-earths and mini-Neptunes around sun-like stars that is consistent with the observed stellar mass dependence in the Kepler planet occurrence rates of F,G,K and M stars.

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Potential Habitability as a Stellar Property: Assessing the Habitable Histories of Stellar Systems

october 4 , 2021   |   12 pm noon   |   Zoom
Noah Tuchow, Penn State University

 

ABSTRACT

Future exoplanet direct imaging missions, such as HabEx and LUVOIR, will select target stars to maximize the number of Earth-like exoplanets that can have their atmospheric compositions characterized. Because one of these missions’ aims is to detect biosignatures, they should consider the long-term habitability of planets around these stars. It is essential to consider whether a planet has been consistently habitable throughout its history or if it only became habitable recently and entered the habitable zone due to the host star’s evolution. We term this latter class of planets Belatedly Habitable Planets, and emphasize that their habitability remains ambiguous and a rich area for future research.
We have developed a framework for computing relative biosignature yields among potential target stars, given a model of habitability and biosignature genesis, and planetary occurrence rates. For different model choices we find that the stellar populations preferred by our metrics vary drastically in terms of stellar masses and ages. The most physically motivated models for biosignature occurrence depend on the duration that a planet has been habitable, which requires precise stellar evolutionary tracks to accurately assess. We analyze the sensitivity of our biosignature yield metrics and other derived stellar properties, such as masses and ages, to stellar model uncertainties and systematic uncertainties in observed stellar properties. We determine the required precision needed to rank target stars according to our long-term habitability metrics and the extent to which obtaining more precise stellar properties decreases the uncertainty in relative biosignature yields.

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inflated Eccentric Migration of evolving gas giants: Accelerated formation and destruction of hot and warm Jupiters

october 11 , 2021   |   12 pm noon   |   Zoom
Mor Rozner, Azrieli Fellow, Physics DepartmentTechnion – Israel Institute of Technology

 

ABSTRACT

Gas giants end the core accretion phase inflated, with radii that could exceed 4RJ. During their evolution, they cool down and contract to their final size, in typical Kelvin-Helmholtz timescales, such that they remain inflated for a major part of their dynamical evolution. The inflation significantly reduces the migration timescales and by that increases the fraction of formed warm Jupiters and leads to enhanced rates of tidal disruption. In this talk, I will review the major challenges in hot and warm Jupiter formation and describe the inflated migration model and its implications.

I will introduce a coupled thermal-dynamical semi-analytical and numerical models that account self-consistently for the contraction and the migration and their mutual effect. Finally, I will discuss the effects of initial inflation on the formed hot and warm Jupiters population and future prospects. 
 
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Dense Gas Formation via Collision-induced Magnetic Reconnection

october 18 , 2021   |   12 pm noon   |   HYBRID (Zoom+In person)
Shuo Kong, Steward observatory, University of Arizona

ABSTRACT

A unique filament is identified in the Herschel maps of the Orion A giant molecular cloud. The filament, which we name the Stick, is ruler-straight and at an early evolutionary stage. Transverse position–velocity diagrams show two velocity components closing in on the Stick. The filament shows consecutive rings/forks in C18O channel maps, which is reminiscent of structures generated by magnetic reconnection. We propose that the Stick formed via a collision-induced magnetic reconnection (CMR) mechanism. We use the magnetohydrodynamics code Athena++ to simulate the collision between two diffuse molecular clumps. The clump collision produces a narrow, straight, dense filament with a factor of >200 increase in density. The production of the dense gas is seven times faster than freefall collapse. The dense filament shows ring/fork-like structures in radiative transfer maps. Cores in the filament are confined by surface magnetic pressure. CMR can be an important dense-gas-producing mechanism in the Galaxy and beyond.

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two populations in the Corona australis complex

october 25 , 2021   |   12 pm noon   |   HYBRID (Zoom+In person)
taran Esplin, Steward observatory,  University of arizona
ABSTRACT

We have performed a census of the young stellar populations near the Corona Australis molecular cloud using photometric and kinematic data from several sources, particularly Gaia EDR3, and spectroscopy of hundreds of candidate members. We have compiled a catalog of 393 members of Corona Australis, (39 at >M6), 293 (36) of which are spectroscopically classified for the first time in this work. We find that Corona Australis can be described in terms of two stellar populations, a younger one (few Myr) that is partially embedded in the cloud (the Coronet Cluster) and an older one (~15 Myr) that surrounds and extends beyond the cloud (Upper Corona Australis). These populations exhibit similar space velocities, and we find no evidence for distinct kinematic populations in Corona Australis, in contrast to a recent study based on Gaia DR2. The distribution of spectral types in Corona Australis reaches a maximum at M5 (0.15 Msol), indicating that the IMF has a similar characteristic mass as other nearby star-forming regions. Finally, we have compiled mid-infrared photometry from the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope for the members of Corona Australis and we have used those data to identify and classify their circumstellar disks. Excesses are detected for 122 stars, a third of which are reported for the first time in this work.

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A high-resolution (sub-)mm view of protoplanetary disks in Taurus 

november 1 , 2021   |   12 pm noon   |   Zoom
Feng Long, SMA Fellow, Harvard-Smithsonian Center for Astrophysics

ABSTRACT

Planets are assembled from the gas and dust in the disks orbiting around young stars. High-resolution interferometric observations at (sub-)mm wavelengths are recently starting to reveal the details of the planet-forming disks. The frequent detection of dust substructures in disks has transformed our view of disk evolution and the planet formation process. In this talk, I will first summarize results from our ALMA-Taurus disk survey that has revealed detailed dust grain distributions in 32 disks.  This will be combined with ALMA archival data to offer a more complete view of Taurus disks around solar-type stars.  I will then provide a detailed investigation on an interesting circumbinary disk system V892 Tau, for which an improved stellar and disk architecture has been constructed employing ALMA and VLA observations. This could serve as a benchmark system for testing the theories of binary-disk interaction, with important implications for the scaled-down version of the planet-disk interaction. 

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Is there weather on WASP-43b? Searching for variation between phase curves

november 8 , 2021   |   12 pm noon   |  HYBRID (Zoom+In person)
Mathew Murphy, steward observatory, University of Arizona

ABSTRACT

Observations of exoplanet atmospheres, particularly Spitzer/IRAC phase curves, have revealed interesting and surprising insights into the climates of exoplanets. However, these observations have largely assumed the observed atmosphere is in equilibrium, and neglected how weather might cause the atmosphere to change in time. In this talk, I will present results of three phase curve observations of the hot Jupiter WASP-43b which set out to test this assumption. These represent the first repeated Spitzer phase curves of an exoplanet, offering three epochs to test for potential weather. After discussing the results of our observations, I will discuss how they compare to models we ran of WASP-43b’s atmosphere, what these all mean for weather on WASP-43b, and the implications of our findings for interpreting exoplanet observations.

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Observational signatures of the vertical sheer instability

in planet-forming disk CO kinematics

november 15 , 2021   |   12 pm noon  |   HYBRID (Zoom+In person)
Marcelo Barraza, MPIA, heidelberg

ABSTRACT   

The turbulent gas motions in planet-forming disks are crucial for their evolution and are thought to affect the planet formation process significantly. Recent (sub-)millimeter observations show evidence of weak turbulence in the disks’ outer regions. However, the detailed physical mechanism of turbulence in these outer regions remains uncertain. The vertical shear instability (VSI) is a promising candidate mechanism to produce turbulence in the outer parts of the disks. By performing global 3D hydrodynamical simulations of a VSI-unstable disk, and post-processing them to produce synthetic ALMA observations, we studied the non-Keplerian kinematic signatures of the VSI that could be observable with the ALMA interferometer. Characterizing these signatures in high-resolution observations can confirm that the VSI operates in the outer regions of protoplanetary disks. During my talk, I will summarize the efforts studying the kinematic signatures of protoplanetary disks produced by the vertical shear instability, and present our predictions for upcoming ALMA observations of CO isotopologues.

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Observing the Evaporating Atmospheres of Exoplanets in Metastable Helium

november 22 , 2021   |   12 pm noon   |   Zoom
Shreyas Vissapragada, Caltech planetary sciences
ABSTRACT

A majority of the extrasolar planets discovered by transit surveys reside surprisingly close to their host stars, and their atmospheres are so intensely irradiated that they can escape altogether. This critical evolutionary process may play a key role in clearing out the Neptune desert (a dearth of Neptune-mass planets on orbits shorter than five days), but it is relatively difficult to observe. The recent discovery of the planetary metastable helium line, which probes tenuous gas near the wind-launching radius, allows us to place some of the first observational constraints on photoevaporation. In this talk, I will first discuss a novel narrowband photometric technique for studying atmospheric outflows using the Wide-field InfraRed Camera (WIRC) at Palomar Observatory. I will then mention some initial results from our survey of atmospheric escape in gas giant planets on the edge of the Neptune desert, as well as some recent constraints on mass loss in the young V1298 Tau system. I will also discuss how energetic considerations can greatly improve mass-loss inference from helium observations. Finally, I will propose some future directions for atmospheric escape studies.

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observational planet formation

november 29 , 2021   |   12 pm noon   |   Zoom

Ruobing dong, University of victoria

 

ABSTRACT

Planets form in gaseous protoplanetary disks surrounding newborn stars. As such, the most direct way to learn how they form from observations, is to observe them forming in disks. In the past, this was difficult due to a lack of observational capabilities, and planet formation was a subject of theoretical research. Now, thanks to a fleet of new instruments with unprecedented resolving power that have come online in the past decade, we have started to unveil features in resolved images of protoplanetary disks, such as gaps and spiral arms, that may be associated with embedded (unseen) planets. By comparing observations with theoretical models of planet-disk interactions, the properties of still forming planets may be constrained. Such planets help us test planet formation models. I will introduce the current status of this field, observational planet formation, and highlight some of the latest developments.

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The Masses and Metallicities of Cool Giant Exoplanets

december 6 , 2021   |   12 pm noon   |   Zoom
Paul Dalba, NSF fellow, UC Santa CruZ, UC Riverside 

 

ABSTRACT 

The union of the transit and radial velocity (RV) techniques, each of which measures a key exoplanet observable, has strongly guided the early development of exoplanet science. However, the short-period selection bias of the transit method has left a dearth of well characterized exoplanets at wider separations, limiting tests of planetary formation theories and contributing to the knowledge gap separating exoplanet and Solar System science. I will discuss results from the ongoing Giant Outer Transiting Exoplanet Mass (GOT ‘EM) survey, which combines transits and RVs but confronts the transit method’s selection bias by focusing on planets with orbital periods between 100 and 1,000 days. The Kepler and TESS missions have discovered a modest sample of these cool giant planets, most with temperatures well below 500 K, but their characterization is still an area of emerging research owing to their lengthy and logistically challenging follow-up process. I will describe our 3+ year effort to measure over a dozen planet masses and orbital eccentricities with Keck-HIRES as well as our methods to infer their bulk heavy element content. Individually, each giant exoplanet is a valuable stepping stone in the underexplored parameter space between hot Jupiters and the Solar System gas giants. Cumulatively, they offer tentative evidence that the heavy element content within a giant planet depends on its current orbital properties. I will place the results of the GOT ‘EM survey in context with recent Solar System results from Cassini and Juno and highlight exciting opportunities for atmospheric characterization in the near future.

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Spring 2021

The Importance of Photoevaporation in the Evolution of Protoplanetary Discs

January 25, 2021   |   12 pm noon   |   Zoom
Andrew Sellek, University of Cambridge

 

I will discuss two new avenues to characterize directly imaged exoplanets. By coherently interfering light from multiple telescopes, we can achieve angular resolutions that are orders of magnitude better than what can be achieved with single dish telescopes. At the Very Large Telescope Interferometer, we achieved the first detection of an exoplanet with long-baseline interferometry using the GRAVITY instrument. I will present some of our recent results with GRAVITY including the first direct detection of a radial-velocity discovered planet and sub-au spatial resolution sensitivity on circumplanetary disks. Second, I will present first light results from the Keck Imager and Characterizer (KPIC), a series of upgrades to the Keck II adaptive optics system, the NIRC2 imager, and the NIRSPEC spectrograph. I will describe the KPIC instrument and highlight some of the early science results from KPIC including imaging protoplanets in the PDS 70 system and obtaining R~35,000 spectra of the HR 8799 planets.

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Beyond perfect merging: the application of machine learning to giant impacts

February 1, 2021   |   12 pm noon   |   Zoom
Saverio Cambioni, California Institute of Technology

 

In terrestrial planet formation studies, collisions between planetary embryos are commonly assumed to be fully accretionary (“perfect merging”). Decades of hydrocode simulations, however, reveal that perfect merging is unlikely save for a confined subset of impact conditions, and that a higher diversity of outcomes should be expected. In this talk I will review recent developments in the use of machine learning to streamline datasets of high-resolution giant impact simulations into fast-forward “surrogate” giant impact models. I will focus on our application of this technique to improve the realism of terrestrial planet formation and differentiation studies and discuss the relevance to the question of planetary diversity.

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Measuring the Accretion Rate onto the Young Gas Giant Planet PDS 70 b with HST UV and H-alpha images

February 8, 2021   |   12 pm noon   |   Zoom
Yifan Zhou, University of Texas, Austin

 

With its two actively accreting planets, the PDS 70 system offers an excellent laboratory for planet formation studies. So far, the planets’ accretion activities have only been probed through their H-alpha emissions. The hydrogen continuum emissions, which likely carry most of the energy released from the planets’ accretion shocks, are undetermined. To further constrain the accretion-induced emission from these planets, we observed the PDS 70 system with HST in the U (F336W) and the H-alpha bands. By adopting a suite of novel image processing and angular differential imaging techniques, we detected the planet PDS 70 b in both bands with high significance. These results led to the first direct measurement of the Balmer continuum emission from a planetary accretion shock. Our observations also placed an upper limit on the planet’s H-alpha variability over a five-month timescale. In this presentation, I will introduce the observational methods that enabled the detections, demonstrate our new accretion rate measurement, and discuss the new insight into the formation process of PDS 70 b.

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Imaging low-mass planets within the habitable zones of nearby stars

February 15, 2021   |   12 pm noon   |   Zoom
Kevin Wagner, University of Arizona

 

Giant exoplanets on wide orbits have been directly imaged around young stars. If the thermal background in the mid-infrared can be mitigated, then exoplanets with lower masses can also be imaged. This talk will describe the Breakthrough Watch/NEAR program: a ground-based mid-infrared observing approach that enables imaging low-mass temperate exoplanets within the closest stellar system, α Centauri. Based on 100 hours of cumulative observations with the VLT, this method demonstrated sensitivity to warm sub-Neptune-sized planets throughout much of the habitable zone of α Centauri A, which is an order of magnitude more sensitive than state-of-the-art exoplanet imaging mass detection limits. We’ll discuss the possibility of a detection in the dataset, the lessons of NEAR as a pathfinder experiment for other facilities (in particular the LBT and ELTs), and implications for the future of imaging rocky habitable-zone exoplanets from the ground.

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 Exoplanets at High Spatial and Spectral Resolution

February 22, 2021   |   12 pm noon   |   Zoom
Jason Wang, Caltech

 

I will discuss two new avenues to characterize directly imaged exoplanets. By coherently interfering light from multiple telescopes, we can achieve angular resolutions that are orders of magnitude better than what can be achieved with single dish telescopes. At the Very Large Telescope Interferometer, we achieved the first detection of an exoplanet with long-baseline interferometry using the GRAVITY instrument. I will present some of our recent results with GRAVITY including the first direct detection of a radial-velocity discovered planet and sub-au spatial resolution sensitivity on circumplanetary disks. Second, I will present first light results from the Keck Imager and Characterizer (KPIC), a series of upgrades to the Keck II adaptive optics system, the NIRC2 imager, and the NIRSPEC spectrograph. I will describe the KPIC instrument and highlight some of the early science results from KPIC including imaging protoplanets in the PDS 70 system and obtaining R~35,000 spectra of the HR 8799 planets.

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Protoplanetary Disk Rings as Sites for Planetesimal Formation

March 1, 2021   |   12 pm noon   |   Zoom
Daniel Carrera, Iowa State University

 

Axisymmetric dust rings are a ubiquitous feature of young protoplanetary disks. These rings are likely caused by pressure bumps in the gas profile; a small bump can induce a traffic jam-like pattern in the dust density, while a large bump may halt radial dust drift entirely. The resulting increase in dust concentration may trigger planetesimal formation by the streaming instability (SI), as the SI itself requires some initial concentration. In this talk I will present the first 3D simulations that successfully form planetesimals by the SI under physically realistic initial conditions, with realistic particle sizes and dust-to-gas ratio (Z = 0.01), relying only on a pressure bump modeled after those observed by ALMA to trigger planetesimal formation. For cm-sized particles, even a small pressure bump leads to the formation of planetesimals — a pressure bump does NOT need to fully halt radial particle drift for the SI to become efficient. For mm-sized particles, we find tentative evidence that planetesimal formation does not occur. This result, if it holds up at higher resolution, could put strong constraints on where in protoplanetary disks planetesimals can form. Ultimately, however, our results suggest that for cm-sized particles, planetesimal formation in pressure bumps is an extremely robust process.

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3D simulations of photochemical hazes in the atmospheres of hot Jupiters

March 8, 2021   |   12 pm noon   |   Zoom
Maria Steinrueck, LPL, University of Arizona

 

Observations of transiting extrasolar giant planets, from hot Jupiters to mini-Neptunes, show evidence of aerosols in their atmospheres. One suggested mechanism for forming these aerosols is that photochemical processes generate hazes on the dayside. In this talk, I will present results from a 3D general circulation model of hot Jupiter HD 189733b that includes photochemical hazes as passive tracers. The resulting haze distribution shows complex patterns. Contrary to previous predictions, small hazes are more concentrated at the morning terminator than at the evening terminator. I will discuss the 3D haze distribution, comparison to observations and the implications for future observations and modeling efforts.

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Chemistry in embedded disks: setting the stage for planet formation

March 15, 2021   |   12 pm noon   |   Zoom
Merel van t’ Hoff, University of Michigan

 

To address the fundamental questions of how life on Earth emerged and how common life may be in the Universe, it is crucial to know the chemical composition of the planet-forming material. Planets were originally thought to form in > 1 Myr old protoplanetary disks, but studies of both disks and our Solar System show that planet formation already starts much earlier, in disks that are still embedded in cloud material. These young disks, however, are largely uncharacterized. I will present a number of case studies on the physical and chemical structure of young disks, including the first temperature measurements showing that young disks are too warm for CO ice, unlike protoplanetary disks. In addition, I will highlight how we can probe the chemical complexity in planet-forming material, and discuss how complex organic molecules can help us understand the low carbon content of our own Earth.

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Protoplanetary Disks and Clouds in Substellar Atmospheres: Insights from Microphysics

March 22, 2021   |   12 pm noon   |   Zoom
Diana Powell, UC Santa Cruz

 

In this talk, I will provide evidence that protoplanetary disks are more than an order of magnitude more massive than previously appreciated, that the detailed properties of clouds shape observations of substellar atmospheres, and that the physics of modeling clouds gives a new understanding of the solid content in protoplanetary disks. Clouds on extrasolar worlds are seemingly abundant and interfere with observations; however, little is known about their properties. In our modeling, we predict cloud properties from first principles and investigate how the interesting observational properties of hot Jupiters and brown dwarfs can be explained by clouds. Next, I will report on a new set of models that reconcile theory with observations of protoplanetary disks and create a new set of initial conditions for planet formation models. The total mass available in protoplanetary disks is a critical initial condition for understanding planet formation, however, the surface densities of protoplanetary disks still remain largely unconstrained due to uncertainties in the dust-to-gas ratio and CO abundance. I make use of recent resolved multiwavelength observations of disks in the millimeter to constrain the aerodynamic properties of dust grains to infer the total disk mass without an assumed dust opacity or tracer-to-H2 ratio. Finally, I will present new work that combines the microphysics of cloud formation in planetary atmospheres and our new models of protoplanetary disks to show that the observed depletion of CO in well-studied disks is consistent with freeze-out processes and that the variable CO depletion observed in disks can be explained by the processes of freeze-out and particle drift.

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Sizing up protoplanetary disks

March 29, 2021   |   12 pm noon   |   Zoom
Leon Trapman, University of Wisconsin, Madison

 

Although we are certain that planets can be formed, there are still large gaps in our understanding of how they formed. Observations show that exoplanets are found in a large variety of planetary systems, from multiple terrestial planets packed inside the central ~1 AU to several gas giants spread over tens of AU from the central star. The diverse outcomes of planet formation are intimately linked to the protoplanetary in which these planets have formed and grown. To better understand planet formation we should therefore study protoplanetary disks. How does the dust in these disks evolve? Does it grow and drift inward like we expect? And how does the gas evolve? Is disk evolution driven by viscous processes and turbulence or is it driven by disk winds? In my talk I will show how studying the sizes of protoplanetary disks can answer these questions and help us solve the riddle of planet formation.

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Simulating Observations of Protoplanetary Disk Ices

April 12, 2021   |   12 pm noon   |   Zoom
Nick Ballering, University of Virginia

 

Ices play a crucial role in planet formation and the delivery of volatiles to terrestrial planets, yet direct observations of ices in protoplanetary disks have, to date, been limited. Upcoming observational facilities—including JWST, SPHEREx, new SOFIA instrumentation, and potentially OST—will greatly enhance our view of disk ices by measuring their infrared spectral features. I will present a suite of models designed to complement these upcoming observations. The models use a kinetics-based gas-grain chemical evolution code to simulate the distribution of ices in a disk, followed by radiative transfer code using a subset of key ice species to simulate the observations. I will discuss which ice species are readily detectable and how the observable features vary with disk inclination, initial chemical composition, and subsequent chemical evolution. I will also highlight the value of obtaining spatially resolved spectra of edge-on disks (possible with JWST’s integral field units) to constrain the vertical distribution of ices and isolate features from ices closer to the disk midplane.

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Understanding Planetary System Formation Through Astrochemistry

April 12, 2021   |   12 pm noon   |   Zoom
ILSE Cleeves, University of Virginia

 

Historically, our understanding of planet formation and the origins of planets’ compositions has been largely informed by our Solar System. However, we are just one system, and now with facilities like NASA’s Kepler and TESS telescopes, we are discovering a wide variety of planet types and architectures, many of which are unlike our own. In the last five years, the Atacama Large Millimeter/Submillimeter Array has simultaneously revolutionized our understanding of planet formation by imaging disks around young stars at high resolution and with high sensitivity. In this presentation, I will discuss how observations of molecular spectral line emission in protoplanetary disks can shed light on 1) the compositions of future planets; and 2) the key physics governing disk evolution during the first few million years of evolution, to help us move toward a more general picture of planet formation, at home and abroad..

Debate: Direct versus Indirect Evidence: Where are the Planets?

April 26, 2021   |   12 pm noon   |   Zoom
During recent years, our field is being transformed by the advent of ALMA, and by the new generation of spectrographs and extreme adaptive optics systems. These instruments observe a rich variety of structure in protoplanetary disks, which are thought to be the birthplace of exoplanets. However, direct detections of young planets are rare. Do young planets exist within these gas rich disks? How common are they? How does the observed disk population relate to the observed exoplanet population around main sequence stars?
The next origins seminar will be an interactive debate where the first steps of planet formation will be discussed.
We will have short presentations by moderators and will spend most of the time for interactive discussions.
If you would like to add a question for the discussion, you can send us one at:

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Molecules with ALMA on planet-forming scales

May 3, 2021   |   12 pm noon   |   Zoom
MAPS Collaboration
Speakers: Charles Law (Harvard),  Alice Booth (Leiden), Jenny Calahan (University of Michigan), and John Ilee (Leeds).                
Abstract:
Planets form in the dust and gas rich disks around young stars. Observations of molecular emission in these disks informs our understanding of the elemental composition of planets as well as the physical conditions in the planet forming environment. The ALMA Large Program Molecules with ALMA on Planet-forming Scales (MAPS) is designed to expand our understanding of chemistry during planet formation by exploring disk chemical structure down to 10 au scales. The program focuses on high spatial resolution observations of five disks – IM Lup, GM Aur, AS 209, HD 163296, and MWC 480, and targets over 40 molecular lines from 20 species. This seminar will highlight key results from MAPS, focusing on substructure in the gas, disk winds, physical and chemical disk modeling, and observations of organic molecules.

 

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Visible high-contrast imaging of young stellar systems

May 10, 2021   |   12 pm noon   |  Zoom
Sebastian Haffert, University of Arizona
ABSTRACT

In the past decade multiple high-contrast imaging instruments have done surveys of stellar systems. Most of these observations have been targeting the (near) infrared wavelength range. Few observations have been done at optical wavelengths. The commissioning of the Laser Tomography Adaptive Optics (LTAO) system together with the integral-field spectrograph MUSE on the VLT enables novel observation of young stellar objects. In this talk I will give an overview of our recent results where we searched for accreting proto-planets in circum-stellar disks, characterized accreting sub-stellar companions and probe stellar outflows down to AU scales.

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Me and my neighbors. Protoplanetary disk evolution with external disturbances

May 24, 2021
Carlo Manara (ESO)
ABSTRACT

In the last years we have expanded our understanding of when, where, and how planets form. In particular, we are starting to constrain the timescale on which planets form, and to have a better understanding of the properties of their natal disks. Whether these properties of protoplanetary disks are similar in different stellar environments is still matter of debate. The mechanisms driving disk evolution, which are tested by combining spectroscopic and millimetre observations of disks and their stars, can be different in more massive clusters with respect to the nearby low-mass star-forming regions. In this talk I will focus on how we can test disk evolution in dense and massive environments by studying protoplanetary disks around multiple stellar systems with ALMA, the accretion rate to disk mass relation in regions with on-going external photoevaporation, and spatially resolved IFU VLT/MUSE data on proplyds in the Orion Nebula Cluster.

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Fall 2020

Characterizing Young, Cool M-Stars and their Planet-Forming Disks

September 14, 2020   |   12 pm noon   |   Youtube
Jamila Peagues, Harvard University

 

M-stars are the most common hosts of planetary systems in the local Galaxy. Observations of protoplanetary disks around these cool stars are remarkable tools for understanding the environment within which their planets form. In this seminar, we present a small sample of protoplanetary disks around M-stars (spectral types M4-M5). Using spectrally and spatially resolved ALMA observations of a range of molecular lines, we measure the dynamical masses of these stars and characterize the chemistry in their disks. We find that dynamical masses for our sample exceed fiducial stellar evolutionary model predictions, and we use this discrepancy to constrain the nature of young, cool M-stars. In terms of chemistry, we find that the distribution of key molecular probes, which offer insight into the organic chemistry and C/N/O ratios, are different both between and across disks around these M-stars. This diversity is similar to what has been previously observed towards solar-type stars. Overall, we find similar patterns of chemistry between our M-star sample and solar-type disks, and we investigate hydrocarbons as one important possible exception. We also discuss future observations, which are crucial to obtain a holistic view of the chemistry of planet formation around the “coolest” stars.

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The Evolution of Disk Winds and their Impact on Planet Formation

September 21, 2020   |   12 pm noon   |   Youtube
Ilaria Pascucci, LPL, University of Arizona

 

Disk winds are often invoked to explain the evolution and dispersal of protoplanetary disks and are thought to play a critical role in the formation and subsequent migration of planets. Yet, their properties and efficiency are poorly constrained observationally. I will present recent results from our high-resolution optical and infrared surveys of protoplanetary disks in different evolutionary stages targeting disk wind diagnostics. I will discuss some of the basic wind properties that can be inferred from these datasets and first attempts to measure wind mass loss rates. I will conclude by sketching an evolutionary scenario that can explain the data at hand and critical measurements to further test it.

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EXPRES: A Next-Generation Spectrograph

September 28, 2020   |   12 pm noon   |   Youtube
Lily Zhao, Yale University

 

EXPRES (the Extreme PREcision Spectrograph) is a R~137,000, fiber-fed, optical spectrograph installed at the 4.3-m Lowell Discovery Telescope near Flagstaff, Arizona. I will give an overview of the optical design, commissioning, and software development that has gone into EXPRES. The instrument itself has demonstrated a stability of 4-7 cm/s. We have constructed a flat-relative, optimal-extraction based pipeline that returns on-sky, single-measurement precision of ~30 cm/s for observations with per-pixel S/N of 250. I will highlight Excalibur, a novel hierarchical, non-parametric method for wavelength calibration. Recent EXPRES data of known planetary systems show sub-m/s residual RMS. EXPRES data is also being used for a community-wide “EXPRES Stellar Signals Project” to diagnose stellar photospheric velocities.

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Untangling the Galaxy

October 5, 2020   |   12 pm noon   |   Youtube
Marina Kounkel, West Washington University

 

Gaia DR2 provides unprecedented precision in measurements of the distance and kinematics of stars in the solar neighborhood. Through applying hierarchical clustering on 5D data set (3D position + 2D velocity), we identify a number of clusters, associations, and comoving groups within 3 kpc. Through leveraging machine leanring techniques, we can estimate the ages of these stars with pseudo-isochrone fitting. Furthermore, supervised learning then allows for identification of isolated pre-main sequence stars that cannot be recovered through clustering. With these efforts combined, we can produce to date the largest catalog of stars with known ages, allowing for investigation of star formation history of the solar neighborhood, such as identifying a ring of stars with ages of up to 40 Myr tracing the outer edges of the Local Bubble that has likely been responsible for the formation of the Gould’s belt. Most of the young stars are commonly found to be filamentary or string-like populations, oriented in parallel to the Galactic plane, and some span hundreds of parsec in length. Most likely, these strings are primordial, tracing the morphology of filamentary clouds that produced them, rather than the result of tidal stripping or dynamical processing. The youngest strings (<100 Myr) tend to be orthogonal to the Local Arm. Stars in a string tend to persist as comoving for time scales of ~300 Myr, after which most dissolve into the Galaxy. These data shed a new light on the local galactic structure and a large-scale cloud collapse.

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ELT Imaging of Protoplanetary Disks and, Eventually, Protoplanets

October 12, 2020   |   12 pm noon   |   Youtube
Josh Eisner, Steward Observatory, University of Arizona

 

The Large Binocular Telescope Interferometer (LBTI) provides the resolution of a 23-m telescope, and can be used now to provide ELT-scale observations of bright protoplanetary disks. We employ the technique of non-redundant masking interferometry, along with adaptive optics and co-phasing systems, to achieve diffraction-limited imaging with this large telescope. Co-phased LBTI operation is currently only possible for bright targets, and we have therefore observed bright protoplanetary disks to date. After presenting the images we have obtained and discussing the scientific implications of these data, I will describe our current work to enhance the LBTI sensitivity, and future plans to extend these ELT imaging observations to planets that are still forming in young protoplanetary disk systems.

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Linking the formation of terrestrial planets and super-Earths with pebble accretion

October 19, 2020   |   12 pm noon   |   Youtube
Michiel Lambrechts, Lund Observatory

 

Super-Earths are found around at least a third of all solar-like stars. However, the origins of this class of planets has remained unclear. Here, we argue that these super-Earth systems are not simply scaled-up versions of classic terrestrial planet formation where the final growth stages are dominated by giant impacts. Instead, we show – using N-body simulations – how super-Earth systems form by the combined mechanisms of pebble accretion and type-1 migration. Rocky embryos grow larger than the Earth by accreting pebbles, migrate to the inner edge of the gas disc, where these planets pile up, and continue to grow until reaching the pebble isolation mass of around 10 Earth masses. After the gas disc dissipates, these compact systems typically become unstable and the original resonant chains are broken. In protoplanetary discs with a moderately reduced mass in pebbles (by a factor 2), or discs with giant planets halting the flux of pebbles, we instead recover a formation channel for systems of terrestrial-like planets. We explore this latter scenario in more detail in the context of the Solar System, using novel GPU-accelerated N-body simulations. An initial distribution of Ceres-mass seed planetesimals, with a total mass of about two Mars masses, is placed in either a narrow ring around the water iceline or throughout the terrestrial zone. Subsequently, this planetesimal population evolves through mutual collisional mergers. The handful of large bodies that grow to Mars in mass complete their growth by efficient pebble accretion, with their final mass depending on the available pebble reservoir before disc dissipation. In this way, we show how analogues to Mercury, Venus, the Earth, and Mars could have formed. This scenario, which argues for the terrestrial protoplanets growing to near completion in the gas disc, appears to be consistent with novel cosmochemical results (e.g. Schiller et al 2018).

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Planet-disk interaction in the era of high-resolution observations: the role of thermodynamics

October 26, 2020   |   12 pm noon   |   Youtube
Jaehan Bae, Carnegie DTM

 

Recent high-resolution observations of protoplanetary disks have imaged a plethora of substructures, including concentric rings/gaps and spiral arms, which hint at on-going planet formation. In this talk, I will introduce recent improvements in our understanding of planet-disk interaction theories. In particular, I will highlight the importance of using more realistic thermodynamics in numerical simulations to fully capture the interaction between planets and their birth disks. I will show that the cooling of the gas in the surface layers and outer regions of protoplanetary disks can be limited due to infrequent gas-dust collisions. The use of the isothermal equation of state or rapid cooling, which has been common in protoplanetary disk simulations, is therefore not justified. I will present a few examples of how the collision-limited slow cooling can change the outcome of planet-disk interaction and discuss their implications.

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Imaging and Surveying Spotted Stars

November 9, 2020   |   12 pm noon   |   Youtube
Rachael Roettenbacher, Yale University

 

For stars with convective outer layers, stellar magnetism manifests as dark starspots–localized regions of stifled convection. Starspots affect measurements of fundamental stellar parameters, including temperature and radius, which lead to inaccurate estimates of age and mass. Additionally, starspots have been shown to mimic and obscure detections of planets. By imaging stellar surfaces, we begin to disentangle the signatures of stellar magnetism. The imaging efforts discussed here feature aperture synthesis imaging using interferometric data collected with the MIRC-X beam combiner at Georgia State University’s Center for High Angular Resolution Astronomy (CHARA) Array with sub-milliarcsecond resolution. Using this technique and others, I image active stars to detect magnetic structures. Here, I will discuss this work and new extensions to survey spotted stars in order to understand how stellar magnetism affects stellar parameters, impacts the evidence and characterization of companions, accounts for long-term changes in the flux of active stars, and differs from the Sun for stars with large convective envelopes.

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Observing Disk Accretion in Action

November 16, 2020   |   12 pm noon   |   Youtube
Joan Najita, NOIRLab

 

Physical processes that redistribute or remove angular momentum from protoplanetary disks can drive mass accretion onto the star and affect the outcome of planet formation. Despite ubiquitous evidence that disk are accreting, the process(es) responsible remain unclear. I will describe new results from that appear to show disk accretion in action: rapid inflow of molecular gas at the surface of a protoplanetary disk. High-resolution mid-infrared spectroscopy of the Class I source GV Tau N reveals a rich redshifted absorption spectrum of individual lines of C2H2, HCN, NH3 and H2O. The properties of the absorption indicate that the flow carries a significant accretion rate, comparable to stellar accretion rates of active T Tauri stars. The results may provide evidence for supersonic “surface accretion flows,” which have been found in MHD simulations of magnetized disks.

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Linking the physics of star and planet formation

November 23, 2020   |   12 pm noon   |   Youtube
Andrew Winter, Humboldt Fellow, Heidelberg University

 

The picture of planet formation proceeding in an isolated star-disc system has been strongly challenged by numerous findings, both old and new. Most recently, with the benefit of a wealth of new instruments, we are beginning to quantify the importance of the environment for the formation and evolution of planets. In this talk, I will outline a few mechanisms that may drive environmentally dependent planet properties, with a focus on external photoevaporation by neighbouring massive stars. I will show how the winds driven by strong external UV fields can deplete the available protoplanetary disc material, and leave imprints on the population that may be used to infer the star formation history of a region. By constraining mass-loss rates in these winds, I will also show how discs in strong UV environments can be used to probe angular momentum transport in PPDs. Finally, I present recent results demonstrating that the architecture of exoplanetary systems, and in particular hot Jupiter occurrence, is dependent on their host star’s kinematic environment. This links to recently found correlations between hot Jupiter occurrence and binary fraction, indicating a dynamical origin for their migration to short period orbits. I conclude that growing evidence suggests the known exoplanet demographics are unlikely to be the consequence of isolated formation, and this must be taken into account for population synthesis models.

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Utilizing Kepler and K2 to Advance Exoplanet Demographics

November 30, 2020   |   12 pm noon   |   Youtube
Jon Zink, UCLA

 

Over the course of several years the Kepler mission, which continuously collected photometric data from a single patch of the sky, provided a uniform set of transiting exoplanet detections. This catalog remains the gold standard for transiting exoplanet occurrence rate studies. However, 18 additional fields of data, sampling a variety of Galactic latitudes, were collected following the malfunction that led to the end of the Kepler prime mission. Better known as the K2 mission, these fields provide a unique opportunity to understand how exoplanet occurrence is affected by Galactic latitude, stellar metallicity, and stellar age. With a fully automated pipeline now able to detect and vet transit signals in K2 data, we can measure the sample completeness and reliability. Correspondingly, I will present the first uniform analysis of small transiting exoplanet occurrence outside of the Kepler field. Additionally, with the full K2 sample now processed, I will discuss how we can incorporate this new catalog of planets into our current demographics analysis to expand our understanding of system architecture and planet formation mechanisms.

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The GM Aurigae Disk: Cold, Massive and Gravitationally Unstable?

December 7, 2020   |   12 pm noon   |   Youtube
Kamber Schwarz, NASA Sagan Fellow, LPL, University of Arizona

 

Protoplanetary disk gas mass remains one of the most difficult disk properties to constrain. With much of the protoplanetary disk too cold for the main gas constituent, H2, to emit, alternative tracers such as dust, CO, or the H2 isotopologue HD are used. Further, recent surveys reveal many disks have low CO-to-dust ratios, suggestive of substantial chemical evolution. Thus, determining the basic disk properties of disk mass, temperature, and CO abundance requires the use of multiple tracers. In this talk I will discuss results from my recent study of the protoplanetary disk GM Aurigae as part of the ALMA large program “Molecules with ALMA at Planet-forming Scales.” Using new and archival ALMA observations, we construct a disk physical/chemical model which reasonably reproduces the spatially resolved CO isotopologue emission, millimeter dust continuum, and the unresolved HD detection from Herschel. Our best fit model favors a large, cold protoplanetary disk with a mass between 0.2 and 0.3 solar masses.

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Thresholds for Planetesimal Formation by the Streaming Instability

December 14, 2020   |   12 pm noon   |   Youtube
Rixin Li, Cornell University

 

A critical step in planet formation is to build super-kilometer-sized planetesimals out of dust particles in gaseous protoplanetary disks. The origin of planetesimals is crucial to understanding the Solar System, exoplanetary systems, and circumstellar disks. In this talk, I will present our most recent work on quantifying the physical conditions needed by the Streaming Instability (SI) to aerodynamically concentrate solids in disks and produce planetesimals. Specifically, we focus on two parameters that control the SI behaviors: particle size and metallicity (i.e., solid abundance relative to the gas). Our high-resolution simulation results pinpoint a metallicity threshold as a function of particle size and find that planetesimal formation can occur even at sub-solar metallicities. I will also show how our results can be applied to general turbulent disk models. Such a threshold prescription is validated by one of our other recent work, where we used forced turbulence simulations to study how the interaction between the SI and intrinsic gas-phase turbulence affects planetesimal formation. Finally, I will describe our attempts to use the linear theory to understand these thresholds and discuss the implications of our results on planet formation and early stages of disk evolution.

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Finding the Missing Worlds: Integrated Analysis of Multi-planet Systems and Applications to TESS and Nearby Systems

August 31, 2020   |   12 pm noon   |   Youtube
Jeremy Dietrich, Steward Observatory, University of Arizona

 

Multi-planet systems provide a wealth of data for exoplanet science, but our understanding of them is still incomplete. By analyzing these systems further, we can gain insight into large-scale information that is not fully explored, such as complete orbital architectures, planet formation pathways, and potential for habitability. In order to efficiently combine data across multiple domains, we developed the DYNAmical Multi-planet Injection Tester (DYNAMITE). DYNAMITE utilizes the incomplete but specific information gathered from multi-planet systems along with population-level statistics to predict the locations, sizes, and natures of previously unknown planets in these systems. DYNAMITE performs an integrated analysis on multi-planet systems individually and in ensembles, and produces testable predictions for planet parameters that can guide archival searches and optimize follow-up observation strategies. Here we share the predictions for a sample of TESS multi-planet systems, as well as predictions for multiple undetected planets in the tau Ceti system, including a possible habitable-zone planet. In the future, we will expand and refine the analysis and prediction space further, investigating planetary populations and probing even more systems for elusive hidden worlds.

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Summer 2020

Testing Earth-like Atmospheric Evolution on Exo-Earths

June 8, 2020   |   12 pm noon   |   Youtube
Alex Bixel, Steward Observatory, University of Arizona

 

Earth’s atmosphere has evolved dramatically from an initially reducing state to an atmosphere rich in biologically produced oxygen. If this type of evolution is typical for inhabited planets, then a positive correlation might exist between the ages of inhabited planets and the fraction which have oxygen. In this talk, I’ll discuss the potential of future space telescopes to test this hypothesis, including optimal age-based target selection strategies and the relevance of “false positive” (i.e. non-biological) oxygen sources.

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Nautilus: A Giant Space Telescope with a New Optical Technology for Large-Scale Biosignature Surveys

June 15, 2020   |   12 pm noon   |   Youtube
Dániel Apai, Steward Observatory / Lunar and Planetary Laboratory

 

Thorough, population-level understanding of habitable and inhabited planets requires studying large samples of  planets. However, the very slow growth of the diameters of space telescopes and their very high costs remain limiting factors for biosignature studies and the broader astrophysics. I will present the Nautilus Space Observatory concept that is designed to characterize the atmospheres of 1,000 exo-earth candidates via transmission spectroscopy. Nautilus uses a novel optical technology: Multi-order diffractive-refractive engineered material (MODE) lenses. MODE lenses provide ultralight and easier-to-fabricate alternatives to primary mirrors and, thus, enable a new paradigm for very large space telescopes. Our long-term goal is to develop a space telescope with a light-collecting area equivalent to that of a 50m-diameter space telescope, within the budget  of a Flagship-class mission. I will show our current technology development program, MODE lens prototypes, and supporting facilities, describe the Nautilus Space Observatory and its science scope.

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SUBSTRUCTURE IN TRANSITION DISKS

June 22, 2020   |   12 pm noon   |   Youtube
Stefano Facchini, European Southern Observatory (ESO)

 

High angular resolution observations of mm-bright protoplanetary disks are showing a broad variety of substructures, with a clear predominance of concentric rings. While mm thermal emission provides key information on the mid-plane properties of planet forming disks, scattered light observations in the NIR are a unique diagnostics of the surface layers and of the very inner regions of disks, which determine the illumination pattern onto the outer regions. In this talk, I will focus on the complementarity of (sub-)mm, NIR imaging and optical photometric observations of disks showing large cavities in the dust distribution, and thus prime targets to observe giant planets interacting with their natal environment. In particular, I will show and discuss new ALMA and VLT/SPHERE data showing substructures in transition disks in their density and velocity structure that are suggestive of planet (or binary)-disk interactions and on-going planet-formation.

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On the diversity of asymmetries in gapped protoplanetary disks

July 6, 2020   |   12 pm noon   |   Youtube
Nienke van der Marel, University of Victoria

 

Protoplanetary disks with large inner cleared dust cavities, also called transition disks, are thought to host massive planetary or substellar companions. These transition disks show a range of structures in the millimeter dust continuum, including asymmetries and one or multiple rings, caused by dust trapping in pressure bumps, and potentially vortices or horseshoes. However, it remains unclear why these asymmetric features appear in some disks and not in others. I will present a possible explanation for this phenomenon, based on the analysis of a sample of 16 disks with large scale dust rings and asymmetries using the local gas surface density profile as constrained by CO isotopologue data. The presence of companions in these disks is deduced from the gas gaps seen in 13CO intensity maps, warps seen in 12CO kinematic maps and spiral arms in scattered light. I will present the different constraints that each of these images provides for the companion mass (substellar or Super-Jovian), and compare them with the limits derived from direct imaging. Furthermore, I will discuss why spiral arms are only seen in some disks. Finally, I will put the transition and ring disks in the larger context of disk dust mass evolution in nearby star forming regions, revealing evidence for separate evolutionary pathways.

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Detecting Complex Organic Molecules in Starless and Prestellar Cores

July 13, 2020   |   12 pm noon   |   Youtube
Samantha Scibelli, Steward Observatory, University of Arizona

 

Before stars like our Sun are born, they are conceived inside dense clumps of gas and dust known as starless and gravitationally bound prestellar cores. Because prestellar cores are at one of the earliest stages of star formation, we can learn a lot about initial chemical conditions. The detection of complex organic molecules (COMs) toward these cores has sparked interest in the fields of astrochemistry and astrobiology, yet detection rates and degrees of complexity within a larger sample of cores (i.e., more than a few) have not been fully explored. With the Arizona Radio Observatory’s 12m telescope, we looked for COMs in 31 starless and prestellar cores, spanning a wide range of dynamical and chemical evolutionary stages, all within the localized L1495-B218 Taurus Star Forming Region. Regions with similar environmental conditions, such as within Taurus, allow for robust comparisons to be made between cores. We found a prevalence of COMs, detecting methanol (CH3OH) in 100% of the cores targeted and acetaldehyde (CH3CHO) in 70%. A deep survey in the nearby young prestellar core L1521E exposed additional complexity, with detections of even larger molecules including dimethyl ether (CH3OCH3), methyl formate (HCOOCH3) and vinyl cyanide (CH2CHCN). We find organics are being formed early and often along the filaments and within starless and prestellar cores in the Taurus Molecular Cloud and that these organics are abundant in the raw material hundred of thousands of years before protostars and planets form.

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Ultra-Hot Jupiters: Revealing the Atmospheres of a Novel Class of Exoplanets

July 20, 2020   |   12 pm noon   |   Youtube
Megan Mansfield,  The University of Chicago

 

Hot Jupiters are compelling targets for thermal emission observations because their high signal-to-noise allows precise atmospheric characterization. Theory originally predicted that cooler planets would show absorption features in their secondary eclipse spectra due to having uninverted atmospheres, while warmer planets would have inverted atmospheres causing emission features in their eclipse spectra. I first discuss our group’s early observations of ultra-hot Jupiters, which led to the realization that these hottest exoplanets are a distinct class with unique high-temperature chemistry. I present new models which take into account this new high-temperature chemistry, and show how they can explain the featureless spectra we observe in many ultra-hot Jupiters. However, observed hot Jupiters still show a surprising level of diversity in their eclipse spectra. To further examine this diversity, I perform a population study of all secondary eclipse observations of hot Jupiters with the Hubble Space Telescope (HST). From this population study I propose that the spectra of hot Jupiters can be explained through compositional diversity in their atmospheres.
In the coming years we will have the opportunity to study hot Jupiter atmospheres in even more detail using the James Webb Space Telescope (JWST). In particular, JWST will provide the unique capability to perform spectroscopic eclipse mapping, which will allow us to map the atmospheres of hot Jupiters in three dimensions (latitude, longitude, and altitude). I present a new method to analyze eclipse mapping observations which can be used to interpret these complicated data sets without relying on expectations from circulation models. Finally, I discuss ongoing observations of hot Jupiters which I will be leading in the coming year using both HST and ground-based high-resolution observations.

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Photometry as a Proxy for Stellar Activity in Radial Velocity Analyses

July 27, 2020   |   12 pm noon   |   Youtube
Molly Kosiarek, UC Santa Cruz

 

Stellar activity remains a limiting factor in measuring precise planet parameters from radial velocity spectroscopy. I will present an analysis of simultaneous disk-integrated photometry and radial velocity data of the Sun in order to determine the useful limits of a combined analysis. We used a Gaussian process to fit both datasets and find that the photometry hyperparameter posteriors are relatively stable over time and observe good agreement with the radial velocity hyperparameter posteriors. Our results indicate that simultaneous photometry & radial velocity monitoring can be a useful tool in enhancing the precision of radial velocity surveys. As an example, I will walk through a couple of exoplanets systems where we performed a similar analysis in order to more accurately account for the effect of stellar noise.

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Depletion of Moderately Volatile Elements by Wind-Driven Mass-Loss in the Early Solar Nebula

August 3, 2020   |   12 pm noon   |   Youtube
Debanjan Sengupta, NASA Ames Research Center

 

The pervasive depletion in meteorite parent bodies and terrestrial planets of Moderately Volatile Elements (MVE), having condensation temperatures between ~ 650 – 1350 K, is a long-standing, unsolved puzzle. Processes such as incomplete condensation of the nebular gas, mixing of volatile-rich and volatile-poor meteoritic components, an MVE-depleted parent molecular cloud, or a natural outcome of the mixing of solids during the evolution of the solar nebula have been studied in the past. However, these efforts are yet to reproduce the trend with a wide range of physically self-consistent parameters. In this talk, we test a new hypothesis that Disk Winds, significant in both outer and inner part of the solar nebula, irreversibly remove the vapor phase materials, including the MVEs inside their evaporation fronts in the inner nebula, leaving nearly all forms of more refractory solids behind in larger particles. The inventory in the inner nebula is further replenished by the inward drift of unfractionated solid material from the cooler outer nebula. First, we discuss our 1+1D nebula evolution model for particles and gas with the recent implementations of disk winds, MVEs, and a new thermal opacity prescription consistent with higher temeperatures. The selected MVE species are tracked in both solid and vapor form in the course of our simulations. Next, we discuss how the depletion trend is dependent on the wind mass loss rate, underlying level of global turbulence, and duration of the process. We can best reproduce the depletion trend using a higher mass loss than typically assumed in existing disk wind models, and a relatively short duration. We note that the conditions are reminiscent of so-called FU-or or YSO active stages. We also discuss the effects of porosities of the dust grains and the level of global disk turbulence on the said depletion trends. Finally, we discuss future work.

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Size and substructures in disks around VLMS

August 10, 2020   |   12 pm noon   |   Youtube
Nicolas Kurtovic, MPIA Heidelberg

 

To improve our understanding of planet formation in disks around very low mass stars (VLMS), we aim to study the substructures and extension of VLMS disks located in the Taurus SFR. To achieve this goal, we combine archival and new 0.87mm ALMA data of 6 bright disks, with a final spatial resolution of about 0.1”. Our resolution and sensitivity is enough to resolve the continuum in all the sample, with sizes (R90%) ranging from 13 to 46au. From visibilities analysis, we find ring-like substructures in 3 disks, and planet masses ranging from 0.4-1.0 Msaturn could explain them. By comparing the ratio of Rgas/Rdust, most of the sample shows a ratio over ~4, which could be evidence of the strong radial drift.

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Disk sub-structures from the variation of disk ionisation

August 17, 2020   |   12 pm noon   |   Youtube
Timmy Deleage, MPIA, Heidelberg

 

Disk ionisation is key in understanding how the magneto-rotational instability (MRI) operates to drive the turbulence in protoplanetary disks. In particular, ionisation drives the so-called “dead zones”.

Previous gas/dust evolution models have shown that dust particles can be efficiently trapped at the dead zone outer edge. Thus, it is a promising mechanism to explain some of the current ALMA observations of protoplanetary disks. However, most of those previous studies parametrised the radial profile of the Shakura-Sunyaev α-parameter, neglecting that it is actually entirely constrained and self-consistently derived from the disk properties and ionisation.

In this talk, I will present a non-ideal MHD model that allows us to obtain a self-consistent α-parameter. Coupling that non-ideal MHD model to the gas/dust evolution model dustpy, we will have the tools to conduct end-to-end simulations that are crucial to understand how the disk properties and ionisation impact on the turbulence, radial drift, settling and diffusion processes of dust particles. Finally, these end-to-end simulations will improve our understanding of the current interpretation of observations.

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Spring 2020

Molecular clouds and star formation: the Big Picture

May 4, 2020   |   12 pm noon   |   Youtube
John Bieging, Steward Observatory, University of Arizona

 

I will highlight results of an extensive series of molecular cloud studies with our radio telescopes (SMT and 12-m) combined with IR observations of Young Stellar Objects and thermal dust emission. These studies encompass the full range of star-forming clouds, from isolated Bok globules to Giant Molecular Clouds. I will present evidence that the rate of star formation follows a power-law of the gas column density down to the parsec scale that is remarkably similar to that inferred for galaxy-wide averages. Predictions of numerical simulations of star formation appear to be consistent with observations. Molecular spectroscopy at high resolution also provides important dynamical information on the processes of stellar feedback that govern star formation rates and efficiencies. Several examples will be presented.

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Carbon during planet formation: From disks and dust to pebbles, planetesimals and planets

May 11, 2020   |   12 pm noon   |   Youtube
Sebastiaan Krijt, (Steward Observatory, Hubble Fellow, NExSS EOS team)

 

Carbon plays a central role in our understanding of protoplanetary disk evolution and (exo)planet formation. In this talk, I will highlight recent studies (mostly from other groups) that use observations of carbon in various forms to shed light on different processes connected to planet formation. I’ll try to present a coherent story while discussing CO depletion in protoplanetary disks, pebble accretion and giant planet atmospheres, (exo)comets, the New Horizons flyby of Arrokoth, the formation of Earth, and polluted white dwarfs.

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Planet formation in stellar clusters

May 18, 2020   |   12 pm noon   |   Youtube
Thomas Haworth, Queen Mary University of London, UK (Lecturer/Royal Society Dorothy Hodgkin Fellow)

 

The main goal of this talk is to get people thinking beyond discs as isolated systems. I will primarily review the growing evidence indicating that the characteristics of planet-forming discs are dependent upon the wider star forming environment. I will then explore the next steps that need to be taken in terms of modelling and observations to cement our understanding of the disc-environment connection and begin to understand how this may imprint upon the resulting planetary populations.

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Looking for the transits of circumplanetary disks

May 26, 2020  |   12 pm noon (MST)   |  youtube
Matthew Kenworthy (Leiden Observatory)
ABSTRACT

In 2007, a 20 Myr old star (called J1407) in the Sco-Cen association underwent a series of complex eclipses that lasted almost two months but showed nightly variations of up to 50%. The best model for this eclipse is a giant ring system filling the Hill sphere of an undetected secondary companion that orbits around this star. This ring system is almost the size of Venus’ orbit, and may be the first detection of a circumplanetary disk in transit which shows hints of exomoon formation.
Since December 2019, a new star has started undergoing a complex eclipse similar to a CPD transit – I will show the latest results of our monitoring campaign from the past few months.
I discuss the search our group is undertaking for more circumplanetary disks and rings, the project bRing which was part of an international campaign searching for material in the Hill sphere of the gas giant planet Beta Pictoris b during its inferior conjunction in 2017 and 2018, and what can we learn by looking for more of these transiting systems in all sky surveys.

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