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
June 11, 2021
Eileen Gonzales (Cornell)
Why Brown Dwarfs Should Be Your Friends: Lessons Learned From Their Atmospheric Retrievals (PDF - 84.3 MB)
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)
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)
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)
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)
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)
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)
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)
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 )
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)
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.
April 30, 2021
Life at NASA (PDF - 60 MB)
March 19, 2021
Finding Planets Around Nearby Stars and A Voice Within Research Collaborations (PDF - 60.8 MB)
February 19, 2021
The Virtual Planetary Laboratory (PDF - 57.3 MB)
January 15, 2021