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404.01 — The Most Extreme Case of Atmospheric Escape Detected on the Warm Neptune GJ 3470b with HST

Vincent Bourrier1

1 Geneva Observatory, University of Geneva (Versoix, Switzerland) Observations of exoplanets during the transit of their host star allow probing the structure and composi- tion of their atmosphere. The intense stellar energy input into exoplanets orbiting close to their star can lead to a dramatic expansion of their upper atmo- sphere, and the ’evaporation’ of large amounts of gas into space. UV observations of hot Jupiters re- vealed the extended exospheres formed by this es- caping gas, and showed that these planets are too massive to lose a substantial fraction of their atmo- sphere. Lower-mass planets are expected to be much more sensitive to evaporation, which has long been thought to play a role in forming the desert of hot Neptunes (a deficit of Neptune-size exoplanets on

very short orbits). I will present the discovery of a giant hydrogen exosphere around GJ3470b, a warm Neptune located at the border of the desert. This is the first UV result of the Panchromatic Compar- ative Exoplanet Treasury (PanCET) survey, a Hub- ble program targeting 20 exoplanets across the entire spectrum. Our numerical simulations of the resolved exospheric transit show that GJ3470b is subjected to mass losses comparable to that of hot Jupiters, mak- ing it the most extreme case of evaporation observed to date. GJ3470b could already have lost up to 40% of its mass over its 2 Gyr lifetime, bringing direct observational confirmation that evaporation shaped the population of close-in exoplanets. I will com- pare GJ3470b with other known evaporating plan- ets and discuss the reasons for its dramatic escape. Our results strengthen the interest of observing the upper atmosphere of exoplanets to determine their properties and understand how they depend on their past evolution. This is particularly important for super-Earth and Earth-size planets, whose lower at- mosphere could be hidden by clouds. The devel- opment of new tracers of atmospheric escape at op- tical/infrared wavelengths opens thrilling perspec- tives for the characterization of exoplanets via their upper atmosphere.

404.02 — A Novel New Method for Measuring Windspeeds on Exoplanets and Brown Dwarfs

Katelyn Allers1; Johanna Vos2; Peter K. G. Williams3; Beth Biller4

1 Physics and Astronomy, Bucknell University (Lewisburg, Penn- sylvania, United States)

2 American Museum of Natural History (New York, New York, United States)

3 Harvard-Smithsonian Center for Astrophysics (Boston, Mas- sachusetts, United States)

4 Institute for Astronomy, University of Edinburgh (Edinburgh, United Kingdom)

Within our solar system, we can directly observe the effects of rapid rotation on the atmospheric physics of the giant planets. Zonal winds, a result of rapid ro- tation and convection, play an important role in the bulk atmospheric flow. This, in turn, can impact at- mospheric chemistry, as evidenced by Jupiter’s dis- equilibrium PH3, which dominates its mid-IR spec- trum. Similar to Jupiter and Saturn, recent studies reveal that many brown dwarfs and directly-imaged exoplanets are also fast rotators with evolving atmo- spheric inhomogeneities. The effects of rotation and convection are starting to be included in efforts to model the atmospheric dynamics of brown dwarfs

and exoplanets. The resulting predictions of wind speed, however, remain relatively untested.

We present the first results of a novel new method for measuring wind speeds on exoplanets and brown dwarfs. Utilizing a combination of radio obser- vations and infrared photometric variability, we present the first observational constraints on wind speed for a cool, cloudless brown dwarf. We discuss the implications of our measurement for models of atmospheric circulation. Looking to the future, we discuss the ways in which new observational facil- ities could extend our method of wind speed mea- surement to other brown dwarfs and exoplanets.

404.03 — Exoplanet atmospheres at high spectral resolution with CARMENES

Enric Palle1

1 Investigacion, Instituto de Astrofisica de Canarias (La Laguna, Spain)

Transmission spectroscopy using high-resolution spectrographs is quickly becoming a major tool to detect and understand planetary atmospheres, from ultra hot Jupiters to Neptunes-size planets. The CARMENES spectrograph started operations in 2016, and since then we have been using it for the study of planetary atmospheres taking advantage of it simultaneous wavelength coverage from visible to near-infrared (0.5-1.7 micron). This has led to sev- eral innovative results, including the first ground- based detections of the He I triplet, allowing the study of exoplanetary tales and scape ratios, or the detection for the first time of the Ca triplet (together with FeII, Na I, and the Balmer series of Hα, Hβ, and Hγ) in the atmosphere of the ultra hot Jupiter (UHJs) MASCARA-2b/KELT20-b. In this talk we will up- date the several He detections on a sample of about a dozen planets, including various levels of stellar ir- radiation and planetary masses. I will also discuss CARMENES’s capabilities for the characterization of UHJs atmospheres, where our results are consistent with theoretical models, predicting a rich day-side ionosphere.

For the SOC: The CARMENES team as a large sam- ple of exoplanets observed (some published some not yet), which can for the first time provide correla- tions between stellar irradiation and the detectability of He I triplet and Hα lines, in some cases both, use- ful for both observers and modelers. I can review the overall results, currently in preparation for a number of publications. For UHJ atmospheres, we can de- tect several atmospheric species with both trasnmis- sion spectroscopy and cross-correlation techniques simultanoeuly, again for a sample of hot planets. So

I think this talk will nicely summaryze several re- sults in two important hot topics of exoplanet atmo- spheres.

404.04 — Unlocking the Hidden Secrets of Hot Jupiter Atmospheres through Near-Ultraviolet Spectroscopy: A Case Study of HAT-P-41b

Nikole Lewis1; Hannah Wakeford2; Ishan Mishra1; David Sing3; Natasha Batalha4; Mark Marley5; Nor Pirzkal2; Thomas Evans6; Jayesh Goyal7; Gregory Henry8; Tiffany Kataria9; Nikolay Nikolov3; Jessica Spake7; Kevin Stevenson2

1 Astronomy, Cornell (Ithaca, New York, United States) 2 STScI (Baltimore, Maryland, United States) 3 JHU (Baltimore, Maryland, United States) 4 UCSC (Santa Cruz, California, United States)

5 NASA Ames (Mountain View, California, United States) 6 MIT (Cambridge, Massachusetts, United States) 7 Exeter (Exeter, United Kingdom)

8 Tennessee State (Nashville, Tennessee, United States) 9 JPL/Caltech (Pasadena, California, United States)

Near-Ultraviolet (NUV, 200-400 nm) spectra of plan- ets hold rich information about the chemistry and physics at work in their upper atmospheres. In the solar system, NUV spectroscopy has been critical in identifying and measuring the abundances of a variety of hydrocarbon and sulfur-bearing species, produced via photochemical mechanisms, as well as oxygen and ozone. To date, less than 20 exoplanets have been probed in this critical wavelength range, with mixed results, limited by the wavelength cov- erage and sensitivity of the workhorse instrument for such studies, HST’s STIS G430L and E230M grat- ings. In HST Cycle 25, our team embarked on a jour- ney to explore the potential of HST’s WFC3/UVIS G280 grism, which offers the highest throughput of all HST’s instruments in the NUV and is up to 25 times more sensitive than its STIS counterparts at 350 nm. The WFC3/UVIS G280 grism does offer one challenge, the presence of overlapping spectral or- ders similar to those of JWST’s NIRISS instrument, which required us to develop new data reduction and analysis techniques. The first target to be ex- plored with this newly unlocked mode on HST was the hot Jupiter HAT-P-41b, which had been previ- ously observed with HST’s STIS G430L grism. Our high-precision spectrum of HAT-P-41b, which com- bines information from both the positive and neg- ative spectral orders, has revealed features in the NUV that cannot be explained by standard equilib- rium chemical models, the presence of aerosols, or stellar activity. Drawing on solar system and stel- lar studies, we considered dozens chemical species

that are known to absorb strongly at NUV wave- lengths. Through detailed atmospheric modeling and retrieval analyses we have uncovered not yet considered chemistry and physics at work in the at- mosphere of HAT-P-41b, which is likely present in many exoplanet atmospheres. In this talk I will de- tail the opportunities that have been opened up with the HST WFC3/UVIS G280 grism in the exploration of exoplanet atmospheres and reveal the once hidden secrets of HAT-P- 41b’s atmosphere.

404.05 — New Theoretical Models for Cloudy Sub- stellar Atmospheres

Caroline Morley1_{; Mark Marley}2_{; Didier Saumon}3 1 Astronomy, University of Texas at Austin (Austin, Texas, United States)

2 NASA Ames Research Center (Mountain View, California, United States)

3 Los Alamos National Laboratory (Los Alamos, New Mexico, United States)

Ample evidence suggests that exoplanets of all kinds have clouds, likely made of many different materi- als from refractory minerals, to silicate dust, to salts, to volatile ices. Clouds are complex to model and challenging to understand from limited observations of exoplanets. Fortunately, planet-mass free-floating objects provide a key venue for understanding cloud formation in substellar atmospheres. These objects have the temperatures of planets but, critically, lack a nearby star, making high signal-to-noise, high pre- cision measurements possible. To understand the physics and chemistry of these atmospheres, we need to compare these high fidelity observed spec- tra to state-of-the-art models. Recent improvements to the ingredients in substellar atmosphere models include new line lists for various important species (methane, alkali metals, water, etc.), as well as up- dated chemistry calculations for a range of metallici- ties and carbon-to-oxygen ratios. Here, we present a new set of substellar atmosphere models for ob- jects warmer than 1000 K including clouds. We show how these models differ from previous cloudy brown dwarf models (Saumon & Marley 2008), and demonstrate how metallicity affects cloudy substel- lar spectra. We present results comparing these models to field brown dwarfs, free-floating plan- ets, and directly-imaged companions, demonstrat- ing how gravity changes cloud properties and emer- gent spectra. Finally, we present a new technique for understanding the compositions and mineralogy of clouds in brown dwarfs using mid-infrared spectro- scopic time-series measurements with JWST. These models will publicly available and provide a critical

tool for the community in the lead-up to the launch of JWST.

404.06 — Infrared Eclipses and Transits of the Best TESS Planets

Ian Crossfield1; Laura Kreidberg2; Diana Dragomir3; Björn Benneke4; Michael W. Werner5; Drake Deming7; Varoujan Gorjian5_{; Xueying Guo}1_{; Courtney Dressing}8_;

Liang Yu1_{; Stephen Kane}6_{; Jessie Christiansen}5_{; David}

Berardo1_{; Farisa Morales}5

1 Physics, MIT (Cambridge, Massachusetts, United States) 2 Harvard University (Cambridge, Massachusetts, United States) 3 MIT/UNM (Cambridge, Massachusetts, United States) 4 U. Montreal (Montreal, Quebec, Canada)

5 JPL (Pasadena, California, United States) 6 UC Riverside (Riverside, California, United States) 7 U. Maryland (College Park, Maryland, United States) 8 UC Berkeley (Berkeley, California, United States)

A key TESS goal is to identify the best exoplanet tar- gets for atmospheric study. We will report on initial results from our large-scale Spitzer program to fol- low up TESS planets with mid-infrared transits and eclipses. Spitzer’s unparalleled infrared sensitivity and photometric stability are allowing us to refine the properties of these new planets and ensure that their transits and eclipses can be recovered for many years to come — e.g., with HST and JWST. Our pro- gram focuses on the smaller (i.e., sub-Jovian) planets for which ground−based observations are impracti- cal and for which JWST spectroscopy will have a high impact. Our most exciting results will include the only secondary eclipse measurements of these sub- Jovian planets until JWST launches. Our program in- cludes eclipse observations of planets from 1–6 Earth radii and equilibrium temperatures from 800-2500 K. In addition, we are producing some of the only thermal phase curves known for such planets. Our program is providing the touchstone sample of TESS planets that will be studied in great detail for many years to come.

404.07 — Peering into the formation history of Beta Pic b with long-baseline interferometry

Mathias Nowak1_{; Sylvestre Lacour}2_{; Paul Mollière}4_{; Ja-}

son Wang3_{; Benjamin Charnay}2 1 Observatoire de Paris (Meudon, France) 2 LESIA, Observatoire de Paris (Meudon, France)

3 Astronomy, California Institute of Technology (Pasadena, Califor- nia, United States)

4 Leiden Observatory (Leiden, Netherlands)

Beta Pictoris is arguably the best-known stellar sys- tem outside of our own. 30 years of study have re- vealed a highly structured circumstellar disk with rings, belts, and a giant planet. But very little is known about how it came into being. In particu- lar, the giant planet beta Pictoris b is known to have played a crucial role in the structuring of the sys- tem, but its formation history remains elusive, de- spite some attempts to settle the cold / hot start question. I will present the first interferometric ob- servations of the giant planet Beta Pic b, obtained with GRAVITY, on the combined four 8.2 m tele- scopes of the VLTI. These observations resulted in the cleanest (S/N > 50), medium resolution (R=500), K-band spectrum of a giant planet ever obtained. I will show that this spectrum, combined with exist- ing low-resolution data, can be used to estimate the planetary C/O ratio, which in turn can be used to trace down the formation history of the planet. In particular, I will present two interpretations of the low C/O ratio obtained, one in the gravitational coll- pase formation paradigm for planet formation, and one in the core-accretion paradigm.