Kepler-16b poster

Presentations Archive

The following are talks given by former ExoExplorers and ExoGuides. Recordings of the webinars, along with transcripts are archived. When available, slides may be downloaded.

ExoExplorer Science Series - 2021

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ExoExplorer Presentations | ExoGuide Talks

ExoExplorer Presentations

June 11, 2021

Eileen Gonzales (Cornell)

Why Brown Dwarfs Should Be Your Friends: Lessons Learned From Their Atmospheric Retrievals (PDF - 84.3 MB)

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Abstract: Brown dwarfs are objects that straddle the mass boundary between stars and planets. With temperatures ranging from ~250-3,000K, brown dwarfs lie in the same range as those of directly imaged exoplanets. Their plentiful and exquisite spectra available make brown dwarfs prime exoplanet analogs for interpreting atmospheric features. Retrievals provide a powerful data-driven technique to delve into questions about the chemistry and atmospheric properties of substellar objects. In this talk, I will discuss lessons learned from spectral retrievals of brown dwarfs using the Brewster retrieval framework. I will present preliminary results from a comparative sample of field sources to the subdwarf SDSS J1416A to determine how their Pressure-Temperature profiles compare to one another to explore what may drive the differences in their spectra. In doing so, I will tell a cautionary tale in trusting retrieval results. Additionally, I will discuss the results of the unusually red L dwarf 2MASS 2224 to explore the nature of clouds and the power of wide spectral coverage.

Kaitlin Rasmussen (U Michigan)

The Hitchhiker’s Guide to the Drake Equation: Past, Present, and Future (PDF - 8.1 MB)

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Abstract: Far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy, the ape-descended lifeforms of an utterly insignificant planet asked a question: "Are we alone?" Frank Drake had an answer: Given a handful of statistics about the local universe, one could calculate the number of intelligent civilizations currently residing in the Milky Way. Today, the Drake Equation poses a serious question in astrophysics: how can we better constrain those statistics? In this talk, I will discuss a variety of approaches to studying the detection, formation rates, and biosignatures of exoplanets, and how they point toward a better understanding of sentient life in the Universe.

May 14, 2021

Jules Fowler (UCSC)

Don't Heckle My Speckle: A Coronagraph Design Study for the SEAL testbed (PDF - 32.1 MB)

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Abstract: In the field of extreme adaptive optics (exAO), we seek to directly image exoplanets from the ground (often by extinguishing speckles of light due to system or environmental factors that may be brighter than the planet itself.) The Santa Cruz Extreme Adaptive optics Laboratory (SEAL) testbed will emulate the W. M. Keck Observatory, to develop and test novel instrumentation and algorithms concerning wavefront sensing, adaptive optics, and coronagraphy. Classical Lyot coronagraphs, in particular, present a fascinating opportunity for a design study, with a wealth of literature from the 2000s that can now be revisited and verified with high fidelity optical modeling using HCIPy. Similarly, Vortex coronagraphs offer improved light suppression while retaining the ability to image close-in companions. In this talk I present a design study for a Lyot and Vortex coronagraph optimized for the SEAL testbed. I will describe my simulations and optimization both in an idealized case and for a realistic case including wavefront, amplitude, and atmospheric errors. I will discuss my final designs for the coronagraph, plans for its implementation in our testbed, and future iterations of this work.

Rachel Fernandes (U. Arizona - LPL)

Exoplanet Demographics Beyond Kepler: Giant Planets with Radial Velocity & Young Planets with TESS (PDF - 11.1 MB)

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Abstract: The Kepler mission has provided detailed exoplanet population statistics for a large range of planet sizes close to their host stars. The first half of my talk will focus on how the completeness-corrected giant planet (~5-20 Re; ~0.1-20 Mj) occurrence rate from Kepler compares with that from the Mayor et al. 2011 radial velocity survey. I will also discuss the discovery of a break in the radial velocity giant planet occurrence rate and its implications for giant planets that be detected by direct imaging. The second half of my talk will focus on the Kepler’s short-period, small planet (~1-1.8 Re) population and how it affects estimates of EtaEarth, the frequency of habitable zone Earth-size planets. I will conclude by presenting our ongoing effort with TESS to de-contaminate the close-in small planet population from photoevaporated mini-Neptunes and thus provide more reliable estimates of EtaEarth.

April 16, 2021

David Coria (U Kansas)

The Missing Link: Connecting Exoplanets and Galactic Chemical Evolution via Stellar Abundances (PDF - 5.7 MB)

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Abstract: This research project seeks to: (1) test the feasibility of determining stellar ages from isotopic measurements; and (2) identify how unexplored stellar abundances correlate with galactic chemical evolution, formation, interior, age, metallicity, activity, and planetary properties for a wide range of host stars. Past isotopic searches have been hindered by limited sensitivity & resolution, strong telluric absorption, and the opacity due to millions of other molecular absorption lines that dominate the observed spectrum of cool stars. Now, however, isotopic abundance analysis is not only possible via high resolution spectroscopy but is also the next logical step for many cool stars. I am measuring the first multi-isotopic (carbon monoxide) abundances in a sample of FGKM stars, to identify possible discrepancies in planetary chemical evolution and accretion models. These isotopic abundance measurements may provide a new means of determining stellar ages and help identify the “missing link” between current Galactic Chemical Evolution models and inconsistent observations. Since most of spectral lines useful in isotopic analysis have low statistical significance and are barely discerned by eye when considered individually, I use a custom list of the strongest lines and create a single line profile for each isotopologue. We create a single, high- S/N line profile by taking the weighted mean, after continuum-normalizing, of each line to create a stacked absorption line. I then create corresponding line profiles for synthetic stellar models corresponding to various enrichments of the targeted isotopologue and compare them to the observed spectra in order to determine final abundances. I will repeat this process for a sample of solar twins, stars in FGK(+M) binaries, stars in known moving groups, and (eventually) any exoplanet host stars that exhibit isotopic signatures. This will provide host star parameters for the currently lacking database as well as the necessary foundations for corollary exoplanet characterization studies and ultimately contribute to the exploration of galactic, stellar, and planetary origins and evolution.

Jason Williams (USC/Carnegie)

The Design and Construction of Henrietta, a high-precision low resolution near-infrared spectrograph to explore exoatmospheres (PDF - 8.4 MB)

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Abstract: When JWST comes online in 2022, it will usher in a golden age of exoatmosphere characterization. Given that available time for exoatmosphere studies will be limited with JWST, it will be impossible for it to survey most exoplanet atmospheres. Thus, it is critically important not only that we have the capability to prioritize the most promising targets for JWST follow-ups, but also multiple instruments available to study the multitude of targets JWST won’t get a chance to survey. These considerations have led to the design of Henrietta, a high-precision, low resolution near-infrared spectrograph for the 1-m Swope Telescope at Las Campanas Observatory. I will talk about why high-precision ground-based spectrophotometry is so challenging in the infrared and how Henrietta’s design choices seek to mitigate these issues. If successful, Henrietta will operate near the photon noise limit and will have ample amounts of telescope time. This will not only provide a consistent stream of targets to JWST, but will also be extremely scientifically productive in its own right - allowing us to begin to place exoplanet atmospheres in a statistical context - and serve as a pathfinder instrument for future ground-based exoatmosphere instruments.

March 12, 2021

Quang Tran (UT Austin)

Establishing the Epoch of Giant Planet Migration (PDF - 62.1 MB)

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Abstract: Most giant planets are expected to have formed beyond the water ice line where their assembly is most efficient. The presence of giant planets interior to ~3 AU around Sun-like stars indicates that inward orbital migration is likely a common phenomenon. However, the processes by which these gas giants arrived at their present-day locations are poorly constrained because radial velocity and transit surveys have largely avoided young stars. As a result, our knowledge of giant planet statistics is primarily confined to old ages (~1-10 Gyr) after most migration has terminated. One solution to find planets around young stars is to move from optical RVs to the near-infrared (NIR), where jitter is reduced as starspot-to-stellar photosphere contrasts are lower than in the optical. In 2018 we launched a precise RV survey of over one hundred intermediate-age (~20-200 Myr) GK dwarfs with the Habitable-Zone Planet Finder near-infrared spectrograph (HPF) at McDonald Observatory's Hobby Eberly Telescope to determine the timescale and dominant physical mechanism of giant planet migration. The Epoch of Giant Planet Migration survey aims to improve our understanding of how and when giant planets migrate to small separations. In this talk, I will summarize results from the first 14 months of this program. We find that RV scatter is significantly reduced in the NIR compared to the optical, facilitating the search for planets around young, active stars.

Amy Glazier (UNC Chapel Hill)

Constraints on Post-Superflare Exo-Auroral Emission with SOAR and the Evryscope Fast Transient Engine (PDF - 43.2 MB)

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Abstract: High-energy particles from M-dwarf superflares -- flares with energy greater than or equal to 1033 erg -- can dramatically impact habitable-zone planets around these cool stars, with possible effects including the excitation of intense aurorae as particles interact with planetary atmospheres. Prior work has demonstrated that Earthlike atmospheres can produce excess emission in M-dwarf spectra, with the star/planet contrast ratio increasing by orders of magnitude in the green 5577-Å auroral line to levels potentially detectable by future surveys. The Evryscopes are gigapixel-scale telescope arrays at Mount Laguna Observatory and Cerro-Tololo Inter-American Observatory; these systems are coupled with the Evryscope Fast Transient Engine (EFTE), which scans Evryscope images in real time for transient phenomena. Together, these systems have the unprecedented ability to identify superflares across the entire sky as they begin, enabling rapid spectroscopic follow-up. With the Evryscopes' all-sky coverage, far more -- and far brighter -- flares are observable than in surveys that focus on individual targets. Using the Goodman spectrograph on the 4.1-m SOAR telescope, we follow the spectroscopic evolution of M-dwarf superflares as they happen, and build a pathfinder survey to constrain upper limits on possible auroral emission from impacted planets. We present our survey here.

February 12, 2021

Caprice Phillips (OSU)

Detecting Biosignatures In Gas Dwarf Planet Atmospheres With JWST (PDF - 30.4 MB )

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Abstract: No Solar System analog planet to super-Earths exists, a class of exoplanets with masses 2-10x Earth’s mass which can retain a hydrogen atmosphere. Super-Earth atmospheres can have different compositions from nitrogen and oxygen dominated atmosphere of Earth. The James Webb Space Telescope (JWST) will offer unprecedented insight into the atmospheric composition of potentially habitable super-Earths through transmission and emission spectroscopy. I will present work on the investigation of NH3 (ammonia, a potential biosignature) detectability on super-Earths with an H2-dominated atmosphere using the Mid-Infrared Instrument (MIRI) and the Near InfraRed Spectrograph (NIRSpec) on the upcoming JWST mission. We use a radiative transfer code, petitRADTRANS, to generate synthetic spectra of optimal targets for observations given their proximity to Earth (<50 pc), radii (1.7-3.36 Earth radii), and equilibrium temperature (< 450 K). I will review the constraints of the MIRI LRS Instrument (flux ratio contrast of host star and planet ~ 10^-4), and discuss optimal targets for this instrument. For NIRSpec, I explore how varying cloud conditions, mean molecular weights (MMWs), and NH3 mixing ratios affects spectral features. Finally, I will discuss the use of PandExo to simulate mock observations with JWST and the detection significance findings for ammonia features with transmission spectroscopy.

Samson Johnson (OSU)

Science Enabled by the Roman Galactic Exoplanet Survey (PDF - 20.9 MB)

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Abstract: The Nancy Grace Roman Space Telescope (Roman) will perform its Galactic Exoplanet Survey when it launches in the mid-2020's. With this first space-based microlensing survey, Roman will be sensitive to planets with orbital separations from roughly 1 AU to those unbound from any host star with masses as low as ten percent that of Earth's. The Roman Galactic Exoplanet Survey will be similar in scale to the Kepler mission, and will produce statistics on exoplanet demographics vital in improving planet formation models that are otherwise inaccessible. In this talk, I will give a brief overview of the Roman Galactic Exoplanet Survey and how it will use microlensing to detect these planets. I will highlight some of the unique insights Roman will give us, including its ability to detect Earth-analog systems and what it can teach us about the presence of free-floating planets in our Galaxy.

ExoGuide Talks

April 30, 2021

Knicole Colón

Life at NASA (PDF - 60 MB)

March 19, 2021

Courtney Dressing

Finding Planets Around Nearby Stars and A Voice Within Research Collaborations (PDF - 60.8 MB)

February 19, 2021

Vikki Meadows

The Virtual Planetary Laboratory (PDF - 57.3 MB)

January 15, 2021

Ian Crossfield

Career Path

ExoExplorer Science Series - 2022

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ExoExplorer Munazza Alam (Carnegie Earth & Planets Laboratory)

The First NIR Transmission Spectrum of HIP 41378 f, a Low-Mass Temperate Jovian World in a Multi-Planet System (PDF - 12.6 MB)

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Abstract: The First Near-Infrared Transmission Spectrum of HIP 41378 f, a Low-Mass Temperate Jovian World in a Multi-Planet System Abstract: We present a near-infrared transmission spectrum of the long period (P=542 days), temperate (T_eq=294 K) giant planet HIP 41378 f obtained with the Wide-Field Camera 3 (WFC3) instrument aboard the Hubble Space Telescope (HST). With a measured mass of ~12 M_earth and a radius of ~9R_earth, HIP 41378 f has an extremely low bulk density (0.09 g/cm^3). We measure the transit depth with a typical precision of 84 ppm in 30 spectrophotometric channels with uniformly-sized widths of 0.018 microns. Within this level of precision, the spectrum shows no evidence of absorption from gaseous molecular features between 1.1-1.7 microns. Comparing the observed transmission spectrum to a suite of 1D radiative-convective-thermochemical-equilibrium forward models, we rule out clear, low-metallicity atmospheres and find that the data prefer high-metallicity atmospheres or models with an additional opacity source such as high-altitude hazes and/or circumplanetary rings. We explore the ringed scenario for this planet further by jointly fitting the K2 and HST light curves to constrain the properties of putative rings. We also assess the possibility of distinguishing between hazy, ringed, and high-metallicity scenarios at longer wavelengths with JWST. HIP 41378 f provides a rare opportunity to probe the atmospheric composition of a cool giant planet spanning the gap between the Solar System giants, directly imaged planets, and the highly-irradiated hot Jupiters traditionally studied via transit spectroscopy.

ExoExplorer Matt Clement (Carnegie Earth & Planets Laboratory)

Solar and Exo-Solar terrestrial planet formation: The bleak prospects for habitability around the smallest stars (PDF - 34.6 MB)

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Abstract: Solar and extra-solar terrestrial planet formation: The bleak prospects for habitability around the smallest stars Abstract: While the solar system's geologic and observational accessibility makes it an unparalleled laboratory in which to study planet formation, exoplanet science has revealed a diverse continuum of evolutionary pathways followed by other systems. Emboldened by these advancements, recent investigations have reevaluated and modernized standard models of planet formation originally based on classic solar system studies. Building from this solar system analogy, contemporary work on exoplanet formation has found that the generic terrestrial planet growth regime is highly sensitive to several key processes. Namely, these include the presence of giant planets, the radial pebble flux, and the formation location of planetary cores. Further invigorating this field, pioneering exoplanet survey missions like Kepler and TESS have spurred a prolific output of multifaceted investigations into the formation of newly detected worlds. Through these advancements, a paradigm shift has occurred in exoplanet science, wherein low-mass stars are increasingly viewed as a foundational pillar of the search for potentially habitable worlds in the solar neighborhood. However, the processes that led to the formation of this rapidly accumulating sample of systems are still poorly understood. Moreover, it is unclear whether tenuous primordial atmospheres around these Earth-analogs could have survived the intense epoch of heightened stellar activity that is typical for low-mass stars. I will summarize our understanding of rocky planet formation and volatile delivery in the solar system, and how these ideas extend to the low-mass regime. I will then present results from new simulations of in-situ planet formation across the M-dwarf mass spectrum. From these calculations, we derive leftover debris populations of small bodies that might source delayed volatile delivery. We then follow the evolution of this debris with high-resolution models of real systems of habitable zone planets around low-mass stars such as TRAPPIST-1.

ExoExplorer Leonardo dos Santos (Space Telescope Science Institute)

An open-source framework to plan and interpret observations of atmospheric escape in exoplanets (PDF - 38.6 MB)

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Abstract: The last couple of years has seen a significant increase in detections of evaporating exoplanets, owing mainly to the discovery of the metastable helium as a probe for atmospheric escape. This process is thought to be an important factor to explain features in the exoplanet population, such as the hot-Neptune desert and the radius valley. While part of exoplanet community, in general, enjoys a swath of open-source codes that help them plan and interpret observations, the same cannot be said about those who study atmospheric escape. At least, not until recently. We developed a new open-source code, named p-winds, with the objective of supplying the community with an easy to use, well-documented tool designed for observations of evaporating exoplanets. In this talk, I will discuss the motivation, implementation, and use cases for p-winds. I will also briefly discuss some recent results that benefitted from this code, and future plans in sight.

ExoExplorer Quadry Chance (University of Florida)

Toward a binary probability for every known exoplanet host star: a statistical framework with Gaia (PDF - 5.5 MB)

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Abstract: The effect of stellar multiplicity on planet formation remains an open question. Investigations carried out using high-resolution imaging and constraints from RV planet searches have indicated that planet formation can be disrupted by close binaries while being relatively unaffected by wide companions. The magnitude and distance-limited nature of those tools have left unexplored companion parameter space in our best planet sample, the Kepler survey. The Early Data Release 3 (EDR3) from the Gaia Mission includes RV measurements of over 7 million targets that can be used to probe this parameter space. Many of these stars are members of unresolved multiple star systems and the effects of these orbits are generally seen as a source of contamination in the Gaia RV catalog. We will demonstrate that the published RV error estimates can provide evidence for the existence of an unresolved stellar companion for Kepler (and other) planet hosts and place constraints on their orbital parameters.

ExoExplorer Eckhart Spalding (University of Notre Dame)

The quest for exoplanet direct imaging with ELT apertures: A hunt for companions with the Large Binocular Telescope (PDF - 58.3 MB)

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Abstract: Direct imaging of exoplanets is a promising route to finding and characterizing exoplanets in the thermal infrared. Currently the technique is most sensitive to massive, young planets on wide orbits. Innovative observing techniques are necessary to probe smaller angles from host stars, or search for older or lower-mass planets. The Large Binocular Telescope (LBT) is in a unique position to push these frontiers in preparation for the era of 30-m-class extremely large telescopes. When light is combined coherently in a "Fizeau" mode between the LBT's twin 8.4-m sub-telescopes, the facility effectively becomes a masked 22.7-m telescope. I will present an observation of the nearby star Altair in this mode, which represents the first LBT Fizeau dataset with a degree of automated phase control. These data constrain the existence of companions of 1.3 M⊙ down to an inner angle of ≈0.15", closer than any previously published direct imaging of Altair. I outline ways forward, in terms of software and physical upgrades, and post-processing with longer integration times.

ExoExplorer Romy Rodríguez Martínez (The Ohio State University)

A reanalysis of the composition of K2-106b, an ultra-short period super-Mercury candidate (PDF - 3.4 MB)

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Abstract: Super-Mercuries are a class of exoplanets with radii less than ~1.5 Re, high bulk densities and relatively large core-mass fractions (CMFs). The study of super-Mercuries will shed light on the composition of low-mass, terrestrial exoplanets as well as on the mechanisms that lead to the formation of iron-rich planets. However, only a few exoplanets have been confirmed as super-Mercuries, in part because of the challenges of obtaining the precise stellar and planetary parameters required to confirm them. I present a reanalysis of the K2-106 system, which contains an ultra-short period, super-Mercury candidate with a density from the literature of 13.1 (+5.4 -3.6) g/cc, approximately twice the density of Earth. We globally model extant photometry and radial velocity of the system and derive a planetary mass and radius that leads to a considerably lower density than previously reported. We derive the host star’s Fe, Mg and Si abundances and combine them with planet interior models to infer the CMF and interior composition of K2-106b. Using a statistical framework, we compared the planet’s CMF as expected from the planet’s density and the CMF as expected from the host star. Our analysis suggests that, although K2-106b has a high density and CMF, it is statistically unlikely to be a super-Mercury.

ExoExplorer Briley Lewis (UCLA)

Small Pieces of the Solar System: Dust, Ice, Pluto, and More (PDF - 4.7 MB)

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Abstract: Small debris, both in and out of our Solar System, provides a window into planet formation. Within our Solar System, we have the Kuiper Belt, icy and dusty debris beyond Neptune, as well as the asteroid belt and Oort Cloud. In 2015, the New Horizons mission provided the first up-close view of a Kuiper Belt Object when it visited Pluto. Pluto’s surface was revealed to be geologically complex, with volatile ices that are mobile on seasonal and longer timescales. Using New Horizons data, we investigated the distributions and movements of ices on Pluto’s surface. Detailed studies of solar system objects, like this work on Pluto’s surface geology, are complementary to our investigations into other planetary systems that harbor debris disks, sometimes referred to as “Exo-Kuiper Belts”. Both provide insight into the processes of planet formation. High-contrast imaging has been key in providing new information about this extrasolar debris, such as measurements of disk extent and morphological asymmetry — information that is not available from infrared excesses alone. However, we are currently limited in our ability to discern composition of debris disks, relying on color measurements and other coarse methods. As characterization capabilities continue to grow, we can expect further discoveries in these complementary fields, especially as new observatories like JWST and the ELTs provide even more highly detailed observations of both solar system objects and debris disks. I will also briefly discuss another small piece of our “solar system” of astronomy—science writing, and pedagogical best practices for integrating writing into physics and astronomy curricula.

ExoExplorer Julia Seidel (ESO)

Observing exoplanet winds (PDF - 15.2 MB)

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Abstract: ESPRESSO, as the first high-resolution spectrograph of the 2020s, has brought a significant increase in line precision, as shown with the re-observation of WASP-76b (Tabernero et al. 2020) and WASP-121b (Borsa et al. 2021), and allows us to move beyond the sole observation of the sodium doublet with a plethora of resolved spectral lines - probing different altitudes in the atmosphere. Using the MERC code (Seidel et al. 2020a), a retrieval tool to determine winds in exoplanet atmospheres, the resolved lines can then be used to retrieve wind patterns directly. Compared to the analysis of the line shape on HARPS data only (e.g. Seidel et al. 2020a for HD189733b), the analysis of the line shape of ESPRESSO data permits to retrieve wind patterns in the upper atmosphere, but additionally also gives us unprecedented observational insights into the lower atmosphere from the line wings (Seidel et al. 2021). In this talk I will provide the community with a guide what we can, and can't. derive about atmospheric winds in exoplanet atmospheres with the current data quality and where our current limits lie as we move to smaller and cooler planets (Seidel et al. 2022). I will also provide a short introduction of ESPRESSO and other ESO instruments that might be useful for the cohort in future observing proposals.

ExoExplorer Kiersten Boley (Ohio State)

Impacts on Planet Formation: Planet Occurrence Rates around Metal-Poor Stars (PDF - 10.5 MB)

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Abstract: Planet formation models predict that below a certain protoplanetary disk metallicity, the surface density of solid material is too low to form planets. Observationally, previous works have indicated that short-period planets preferentially form around stars with solar and super solar metallicities. Given these findings, it is challenging to form planets within metal-poor environments. Due to the target selection process of previous surveys, there is little constraint on planet occurrence rates below [Fe/H] ~ -0.5, which is still higher than the predicted metallicity at which planet formation cannot occur. Expanding upon previous works, we construct a large sample of ~100,000 metal-poor stars with spectroscopically-derived stellar parameters observed by TESS. With this sample, we constrain planet occurrence rates within the metal-poor regime (-1.0 ≤ [Fe/H] ≤ -0.4) placing the most stringent upper limits on planet occurrence rates around metal-poor stars.

ExoExplorer Alison Farrish (GSFC)

Modeling Exoplanet Host Star Magnetic and Coronal Activity (PDF - 1.8 MB)

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Abstract: Exoplanet systems are of interest not only for their potential for habitability, but also in the opportunity they provide for the study of comparative heliophysics. In applying solar- and heliophysics-based modeling tools to exoplanet systems, we can expand our understanding of the influence of stellar behavior on planetary environments and processes such as atmospheric loss. I will discuss my work employing a surface flux transport (SFT) model to examine the dynamics of magnetic flux on the surfaces of cool stars like the Sun and exoplanet host stars of interest. This flux transport modeling approach has been used to examine stellar coronal X-ray emission and other asterospheric properties as a function of host star magnetic activity. I will provide an overview of current efforts to extend this modeling framework to investigate host star EUV emission and stellar wind parameters for a range of exoplanet host stars. Since stellar EUV emission is both a) a key driver of atmospheric loss processes and b) difficult to observe due to interstellar medium extinction, these simulations of energetic coronal emission could fill gaps in our understanding of exoplanet atmospheric evolution caused by this dearth of observational evidence.

ExoExplorer Aarynn Carter (UCSC)

Kickstarting a New Generation of Exoplanet Observations: Early Release Science with JWST (PDF - 32.5 MB)

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Abstract: Following the launch of JWST, in addition to a selection of ongoing commissioning activities, we now stand just months away from the beginning of scientific observations. Dispersed throughout these initial data will be a selection of Director’s Discretionary Early Release Science (ERS) observations which were designed under a primary goal of rapidly informing the community on JWST’s performance and capabilities. With respect to the study of exoplanets, only two ERS programs exist: “The Transit Community Early Release Science Program” (PI: N. Batalha, ERS-1366), and “High Contrast Imaging of Exoplanets and Exoplanetary Systems” (PI: S. Hinkley, ERS-1386). In totality, these two programs will set the tone for JWST exoplanet observations throughout its lifetime. In this talk I will provide an up-to-date overview of both of these programs, the timelines for their data releases, and a description of their technical and scientific goals. Additionally, I will discuss existing and ongoing preparatory work towards the production of a range of science enabling products. These products (e.g. data reduction pipelines, analyses of best practices) are an integral part of the ERS programs and will support JWST investigations throughout Cycle 2 and beyond.

ExoExplorer Aida Behmard (Caltech)

How Common is Planet Engulfment? (PDF - 23.2 MB)

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Abstract: Dynamical evolution within planetary systems can cause planets to be engulfed by their host stars. Following engulfment, the stellar photosphere abundance pattern will reflect accretion of rocky material from planetary cores by exhibiting refractory enhancements in order of condensation temperature $T_c$. Multi-star systems are excellent environments to search for such abundance trends because stellar companions share the same natal gas cloud and primordial chemical composition to within $\sim$0.05 dex. Thus, refractory differences above $\sim$0.05 dex that trend with $T_c$ between companions are a signpost of engulfment. Abundance measurements have occasionally yielded such engulfment signatures, but few observations targeted systems with known planets. To address this gap, we carried out a survey of 36 multi-star systems where one star is a known planet host with the Keck High Resolution Echelle Spectrometer. None of the 36 systems observed exhibit abundance patterns strongly indicative of engulfment events, which could be explained by our modeling efforts that show observable refractory enrichments from 10 $M_{\oplus}$ engulfment events are depleted on timescales of $\sim$1 Gyr for solar-like stars.

ExoGuide Talks

Elisa Quintana (GSFC)

José A. Caballero (CSIC-INTA)

Sarah Rugheimer (Oxford University)

Bruce Macintosh (Stanford University)

ExoExplorer Science Series - 2023

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ExoExplorer Ellis Bogat (U Maryland)

Probing the Outskirts of M Dwarf Planetary Systems with a JWST Cycle 1 Direct-Imaging Survey of Nearby Young M Stars (PDF - 7.5 MB)

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Abstract: The population of giant planets on wide orbits around low-mass M dwarf stars is poorly understood. However, the discovery and characterization of these planets is key to understanding the architectures and evolution of M dwarf planetary systems and places their frequent and potentially habitable inner planets in context. While current ground-based imaging struggles to probe below a Jupiter mass at large separations, the unprecedented sensitivity of JWST NIRCam coronagraphic imaging provides direct access to planets significantly less massive than Jupiter beyond 10 AU around the closest, youngest M dwarfs. In this talk, I will introduce the key aspects of exoplanet direct imaging and present the survey design, observations, and preliminary results of JWST GTO Program 1184, a NIRCam coronagraphic imaging survey of very nearby, young low-mass stars.

ExoExplorer Sean McCloat (U North Dakota)

Modeling the Architecture and Composition of Exoplanetary Systems from Pebble Accretion (PDF - 1.3 MB)

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Abstract: This dissertation models the composition and architecture of planetary systems formed via pebble accretion. The modeling is achieved using a combination of the pebble coagulation model “pebble-predictor” (Drazkowska et al., 2017) and accretion efficiency recipes (Ormel & Liu 2017) to consistently develop the pebble properties and protoplanet formation rates based on disk conditions. The composition of protoplanets is modeled by relating the disk properties to changes across the water ice line and assuming the local composition determines the pebble composition. In this way, the composition of pebbles, their accretion efficiency, and therefore protoplanet composition, are consistently modeled from disk properties. Model outputs are systems of protoplanets with a consistently determined mass, bulk composition, and orbital distance at the protoplanetary disk stage when gas fully dissipates. The dissertation will further explore variations in stellar mass, ice line evolution, and seed mass distributions to explore trends in the occurrence rates of different types and bulk compositions of planets. In this research, I assume a stage of gravitational n-body interactions follows pebble accretion. N-body simulations of this sort can be computationally expensive. Fortunately, simulations encompassing a range of starting system architectures already exist in the genesis models (Mulders et al. 2018). The results of the genesis models are recorded and publicly available in the form of interaction histories between protoplanets, or “collision trees”. This research will compare model outputs to inputs of genesis to determine what conditions, if any, can be followed through the late stages of planet formation and inspect final planetary system bulk composition and architecture.

Alison Duck (Ohio State)

Reanalyzing Kelt-15b: An Exploration of Systematic Errors in Transiting Planets and Their Host Stars (PDF - 6.5 MB)

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Abstract: Transiting planet systems offer the best opportunity to measure the masses and radii of a large sample of planets and their host stars. However, relative photometry and radial velocity measurements alone only constrain the density of the host star. Thus, there is a one-parameter degeneracy in the mass and radius of the host star, and by extension the planet. Several theoretical, semi-empirical, and nearly empirical methods have been used to break this degeneracy and independently measure the mass and radius of the host star and planets(s). We focus our analysis on modelling KELT-15b, a fairly typical hot Jupiter, using each of these methods implemented in EXOFASTv2. As we approach an era of few percent precisions on some of these properties, it is critical to assess whether these different methods are providing accuracies that are of the same order, or better than, the stated statistical precisions. We investigate the differences in the planet parameter estimates inferred when using the Torres empirical relations, YY isochrones, MIST isochrones, and a nearly-direct empirical measurement of the radius of the host star using its spectral energy distribution, effective temperature, and Gaia parallax.

Armaan Goyal (Indiana U)

The Interplay of Mean Motion Resonance and Peas-in-a-Pod Architectures (PDF - 7.6 MB)

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Abstract: Planets orbiting the same star tend to display a striking degree of uniformity in their size, mass, and orbital spacing, exhibiting a “peas-in-a-pod” phenomenon that serves to place invaluable constraints on the formation of multiple-planet systems. In this talk, I shall discuss a pair of statistical analyses that probe the relationship between mean motion resonance (MMR) and the emergence of these peas-in-a-pod architectures. Recent demonstrations of planetary mass uniformity have largely been limited to systems that exhibit strong transit-timing variations (TTVs), and are thus near MMR. Accordingly, I shall present in the first half of this talk a novel demonstration of mass uniformity for a sample of planetary systems entirely devoid of TTVs, suggesting that peas-in-a-pod architectures indeed persist for non-resonant systems as well. While this result may seem to imply that the emergence of peas-in-a-pod architectures occurs agnostically with regard to resonance, the question still remains if the degree of the associated planetary uniformity differs between near-resonant and non-resonant configurations. I shall thus present in the second half of this talk a direct comparison of size uniformity between the two modes, finding that near-resonant planetary configurations display enhanced size uniformity compared to their non-resonant counterparts, both across entire systems and within the same planetary system. These results are broadly consistent with a variety of formation paradigms for multiple-planet systems, though further investigation is necessary to ascertain whether the respective evolutionary channels for non-resonant and near-resonant configurations comprise a singular process or are themselves wholly distinct.

Pa Chia Thao (U of North Carolina Chapel Hill)

Hazy with a Chance of Star Spots: Constraining the Atmosphere of the Young Planet, K2-33b (PDF - 9.4 MB)

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Abstract: Studying the properties of planets across a wide range of ages will help provide insights into the processes that shape their formation and evolution. While all-sky surveys have discovered dozens of young planets (<1 Gyr), their atmospheres remain largely unknown. In this study, we explore the transmission spectrum of K2-33b, the youngest (10 Myr), transiting exoplanet discovered. Using multi-wavelength data obtained from K2, MEarth, HST, and Spitzer, we found that the optical transit depths were nearly 2 times deeper than the near-infrared depths. This difference holds across multiple data sets taken over two years, ruling out issues of data analysis and unconstrained systematics. While surface inhomogeneities on the young star could have contributed to the observed difference, the observed stellar spectra ruled out the required spot coverage fractions. Instead, we found that a tholin haze with carbon monoxide as the dominant carbon carrier provided a better fit to the transmission spectrum. A companion study found that a circumplanetary dust ring can also explain the transit depth difference. Further observations are needed to separate the two scenarios, confirm the presence of CO, and map out the role of spots on the transmission spectrum.

Anjali Piette (Carnegie EPL)

The Observability of Low-Density Lava World Atmospheres: A Window into Super-Earth Interior Compositions (PDF - 7.6 MB)

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Abstract: The super-Earth population spans a wide range of bulk densities, indicating a diversity in interior conditions beyond that seen in the solar system. In particular, a growing population of low-density super-Earths may be explained by volatile-rich interior compositions. Among these, lava worlds, with dayside temperatures high enough to evaporate their surfaces, provide a unique opportunity to probe the diverse surface and interior compositions of super-Earths. In this talk, I will discuss the atmospheric observability of low-density lava worlds, whose bulk densities are consistent with volatile-rich interior compositions. Using self-consistent 1D atmospheric models, I explore the atmospheric structures and thermal emission spectra of these planets across a range of mixed rock vapor/volatile compositions. Spectral features due to both volatile and rock vapor species are present in the infrared thermal emission spectra, though the strength of such features - and whether they appear as emission or absorption features - depends on the dayside temperature and atmospheric composition. In order to assess the observability of such features with JWST, I simulate JWST thermal emission observations and perform synthetic atmospheric retrievals for three promising targets. Detecting volatiles in the atmospheres of these evaporating exoplanets would provide new evidence that volatile-rich interiors exist among the super-Earth population.

Clarissa Do O (UC San Diego)

Constraining the Formation of Directly Imaged Exoplanets By Upgrading the Gemini Planet Imager (GPI)’s Wavefront Sensor (PDF - 6.0 MB)

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Abstract: The Gemini Planet Imager (GPI) is a high contrast imaging instrument designed to directly detect and characterize young, Jupiter-mass exoplanets. After six years of operation at Gemini South in Chile, the instrument is being upgraded and relocated to Gemini North in Hawaii as GPI 2.0. GPI helped establish that Jovian-mass planets have a higher occurrence rate at smaller separations (~1-10 AU), and their formation pathways are still not completely understood. These questions motivate several sub-system upgrades to obtain deeper contrasts particularly at small inner working angles. One of GPI 2.0’s upgrades will be on its adaptive optics system, by replacing the current Shack-Hartmann wavefront sensor (WFS) with a pyramid WFS and a custom EMCCD. Electron multiplying CCDs (EMCCDs) are detectors capable of counting single photon events at high speed and high sensitivity. The upgraded ultra low-noise wavefront sensor is expected to give the adaptive optics (AO) system the capability to achieve high Strehl ratios on stars two magnitudes fainter than the current limit. GPI 2.0 is expected to go on-sky in late 2025. Here I will present on GPI 2.0’s science goals, its adaptive optics upgrades and the latest timeline for operations and current status.

Evelyn MacDonald (U Toronto)

Ambiguities in transit spectra of habitable zone rocky planets due to unknown surface conditions (PDF - 1.6 MB)

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Abstract: JWST will produce transit spectra of several habitable zone rocky planets orbiting M-dwarfs in the coming years. To provide context for interpreting observations, I use a 3D climate model combined with a radiative transfer model to generate synthetic transit spectra for a synchronously rotating rocky planet over a large parameter space of possible climates. Since it will be difficult to constrain a planet’s surface conditions empirically, I systematically vary the planet’s land cover and atmosphere mass in order to characterize the climate uncertainties associated with these parameters. These variations result in a large range of possible climate states featuring significant differences in surface temperature and humidity. I will show that planets in different climate regimes can have similar transit spectra, which means that it will likely be difficult to measure a given planet’s liquid water inventory or the size of its temperate region using transit spectroscopy. Land cover and atmosphere mass are therefore important sources of climate uncertainty to account for when interpreting JWST spectra.

Michelle Kunimoto (MIT)

Diamonds in the Rough: Finding Thousands of New Planet Candidates Around Faint Stars (PDF - 4.9 MB)

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Abstract: The Transiting Exoplanet Survey Satellite mission (TESS) enables the discovery of exoplanets around tens of millions of stars by regularly recording its entire field of view in Full Frame Images (FFIs). However, current TESS planet searches require significant manual inspection efforts to identify planets among transit-like detections, which limits their scope to small subsets of this stellar sample. I will present an ongoing search for transiting exoplanets around all ~20 million stars brighter than T = 13.5 mag that have been observed in TESS FFIs, made possible by the development of a near-fully automated vetting pipeline to efficiently distinguish planets from false positives. This search has uncovered ~2700 TESS Objects of Interest (TOIs), most of which are giant, close-in exoplanets around faint stars not explored by other searches. I will highlight some particularly exciting discoveries, including rare types of exoplanets and intriguing targets for atmospheric characterization. The automated vetting pipeline developed for this project, as well as the new candidates discovered in this ongoing search, will allow TESS to significantly improve the statistical power of demographic studies in the future.

Junellie González Quiles (Johns Hopkins)

Carbon Cycling on the TRAPPIST-1 Planets (PDF - 6.3 MB)

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Abstract: The TRAPPIST-1 planets have become prime targets for studying the habitability of planets around M-dwarf stars. Modeling geochemical cycles in these planets can provide insight on their evolution and their potential for habitability. Through planet formation and long-term tectonic evolution, there is an exchange of volatiles between the interior and the atmosphere of rocky planets. We model the combined deep water and carbonate-silicate cycles to trace the production of different gas species including hydrogen, water, carbon dioxide, and carbon monoxide. We also aim to study how exoplanet interior structure and material properties, like oxygen fugacity, influence the atmosphere of these planets. These outgassing models can help us understand the evolution of the atmospheric composition and its effect on planetary climate. We present the results from our models, which include the atmospheric abundances as well as the surface and mantle temperatures of exoplanets TRAPPIST-1 d, e and f.

Jack Lubin (UC Irvine)

Exploring New Dimensions through Time/Frequency Analysis of RV Datasets with Lia (PDF - 20.7 MB)

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Abstract: One of the most pressing challenges in the new era of Extreme Precision Radial Velocity (EPRV) instruments is to disentangle signals induced by stellar activity from planetary signals. With small exception, planetary signals are distinct from activity signals in that they have a constant frequency, phase, and amplitude. Meanwhile, activity signals may come and go, growing and decaying over a characteristic lifetime, and returning again with possible phase and frequency shifts. Here, we present an approach exploiting this feature: we decompose the RV signal on a basis of apodized sinusoidal functions. Bayesian methods are precise and interpretable but computationally expensive. Periodograms are fast and provide statistics, but are prone to aliasing because they search one signal at a time. Here, we introduce the L1 Apodized Periodogram, L1A or Lia (pronounced like the name, “Leah”). This new software uses an L1 minimization approach, allowing to search for several signals at the same time with a moderate computational cost, to identify and characterize both the periodicity and decay lifetime of signals in a dataset. With a new way to look into our RV data sets, we can gain new insights and better understand the astrophysical origin of signals.

Isabella Trierweiler (UCLA)

Mapping exoplanet compositions using polluted white dwarfs (PDF - 19.2 MB)

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Abstract: A persistent question in exoplanet characterization is whether exoplanetary systems form from similar compositional building blocks to our own. Polluted white dwarf stars offer a unique way to address this question as they provide measurements of the bulk compositions of exoplanetary material. These stars show evidence of recent accretion of rocky bodies in the form of metal lines in their spectra, which tell us about the relative elemental abundances of the accreted material. In this talk I will share a statistical analysis of the rocks polluting white dwarfs and compare their compositions to Solar System rocks, such as chondrites, bulk Earth, and crust. In this study, I find that the majority of the extrasolar rocks are consistent with the composition of chondrites, a result that is supported by the compositions of stars in the solar neighborhood.

ExoGuide Talks

Yamila Miguel (Leiden)

Ben Montet (UNSW)

Néstor Espinoza (STScI)