Origins Seminar Series Event Archive

2021

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.

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.

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.

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.

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.

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. 

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. 

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.

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

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.

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.

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.

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.

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.  

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.

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.

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.

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.

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.

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.

 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.

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.

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.

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.

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.

2020

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.

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.

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.

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.

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.

Imaging and Surveying Spotted Stars

November 9, 2020   |   12 pm noon   |   Youtube

Rachael Rottenbacher, 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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Title

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.

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.

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.

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.

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.

Looking for the transits of circumplanetary disks

May 26, 2020   |   12 pm noon   |   Youtube

Matthew Kenworthy, Leiden Observatory

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.

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.

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.

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.