Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Marshall C. Johnson
Ji Wang
Anusha Pai Asnodkar
Aldo S. Bonomo
B. Scott Gaudi
Thomas Henning
Ilya Ilyin
Engin Keles
Luca Malavolta
Matthias Mallonn
Karan Molaverdikhani
Valerio Nascimbeni
Jennifer Patience
Katja Poppenhaeger
Gaetano Scandariato
Everett Schlawin
Evgenya Shkolnik
Daniela Sicilia
Alessandro Sozzetti
Klaus G. Strassmeier
Abstract： Recent observations have shown that the atmospheres of ultra hot Jupiters (UHJs) commonly possess temperature inversions, where the temperature increases with increasing altitude. Nonetheless, which opacity sources are responsible for the presence of these inversions remains largely observationally unconstrained. We used LBT/PEPSI to observe the atmosphere of the UHJ KELT-20 b in both transmission and emission in order to search for molecular agents which could be responsible for the temperature inversion. We validate our methodology by confirming previous detections of Fe I in emission at $16.9\sigma$. Our search for the inversion agents TiO, VO, FeH, and CaH results in non-detections. Using injection-recovery testing we set $4\sigma$ upper limits upon the volume mixing ratios for these constituents as low as $\sim1\times10^{-9}$ for TiO. For TiO, VO, and CaH, our limits are much lower than expectations from an equilibrium chemical model, while we cannot set constraining limits on FeH with our data. We thus rule out TiO and CaH as the source of the temperature inversion in KELT-20 b, and VO only if the line lists are sufficiently accurate.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Matteo Brogi
Vanessa Emeka-Okafor
Michael R. Line
Siddharth Gandhi
Lorenzo Pino
Eliza M. -R. Kempton
Emily Rauscher
Vivien Parmentier
Jacob L. Bean
Gregory N. Mace
Nicolas B. Cowan
Evgenya Shkolnik
Joost P. Wardenier
Megan Mansfield
Luis Welbanks
Peter Smith
Jonathan J. Fortney
Jayne L. Birkby
Joseph A. Zalesky
Lisa Dang
Abstract： We present high-resolution dayside thermal emission observations of the exoplanet WASP-18b using IGRINS on Gemini South. We remove stellar and telluric signatures using standard algorithms, and we extract the planet signal via cross correlation with model spectra. We detect the atmosphere of WASP-18b at a signal-to-noise ratio (SNR) of 5.9 using a full chemistry model, measure H2O (SNR=3.3), CO (SNR=4.0), and OH (SNR=4.8) individually, and confirm previous claims of a thermal inversion layer. The three species are confidently detected (>4$\sigma$) with a Bayesian inference framework, which we also use to retrieve abundance, temperature, and velocity information. For this ultra-hot Jupiter (UHJ), thermal dissociation processes likely play an important role. Retrieving abundances constant with altitude and allowing the temperature-pressure profile to freely adjust results in a moderately super-stellar carbon to oxygen ratio (C/O=0.75^{+0.14}_{-0.17}) and metallicity ([M/H]=1.03^{+0.65}_{-1.01}). Accounting for undetectable oxygen produced by thermal dissociation leads to C/O=0.45^{+0.08}_{-0.10} and [M/H]=1.17^{+0.66}_{-1.01}. A retrieval that assumes radiative-convective-thermochemical-equilibrium and naturally accounts for thermal dissociation constrains C/O<0.34 (2$\sigma$) and [M/H]=0.48^{+0.33}_{-0.29}, in line with the chemistry of the parent star. Looking at the velocity information, we see a tantalising signature of different Doppler shifts at the level of a few km/s for different molecules, which might probe dynamics as a function of altitude and location on the planet disk. Our results demonstrate that ground-based, high-resolution spectroscopy at infrared wavelengths can provide meaningful constraints on the compositions and climate of highly irradiated planets. This work also elucidates potential pitfalls with commonly employed retrieval assumptions when applied to UHJ spectra.
Peer Review Status:Awaiting Review
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