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arXiv · 2201.02261

Strong H$_2$O and CO emission features in the spectrum of KELT-20b driven by stellar UV irradiation

Guangwei Fu·David K. Sing·Joshua D. Lothringer·Drake Deming·Jegug Ih·Eliza Kempton·Matej Malik·Thaddeus D. Komacek·Megan Mansfield·Jacob L. Bean
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Abstract

Know thy star, know thy planetary atmosphere. Every exoplanet with atmospheric measurements orbits around a star, and the stellar environment directly affects the planetary atmosphere. Here we present the emission spectrum of ultra-hot Jupiter KELT-20b which provides an observational link between host star properties and planet atmospheric thermal structure. It is currently the only planet with thermal emission measurements in the $T_{eq}\sim$2200K range that orbits around an early A-type star. By comparing it with other similar ultra-hot Jupiters around FGK stars, we can better understand how different host star types influence planetary atmospheres. The emission spectrum covers 0.6 to 4.5 $\mu m$ with data from TESS, HST WFC3/G141, and Spitzer 4.5 $\mu m$ channel. KELT-20b has a 1.4 $\mu m$ water feature strength metric of S$_{H_2O}$ = -0.097$\pm$0.02 and a blackbody brightness temperature difference of 528K between WFC3/G141 (T$_b$=2402$\pm$14K) and Spitzer 4.5 $\mu m$ channel (T$_b$=2930$\pm59$K). These very large H$_2$O and CO emission features combined with the A-type host star make KELT-20b a unique planet among other similar hot Jupiters. The abundant FUV, NUV, and optical radiation from its host star (T$_{eff}=8720\pm250$K) is expected to be the key that drives its strong thermal inversion and prominent emission features based on previous PHOENIX models calculations.

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Guangwei Fu, David K. Sing, Joshua D. Lothringer, Drake Deming, Jegug Ih, Eliza Kempton, Matej Malik, Thaddeus D. Komacek, Megan Mansfield, Jacob L. Bean. 2022-01-06. Strong H$_2$O and CO emission features in the spectrum of KELT-20b driven by stellar UV irradiation. https://doi.org/10.3847/2041-8213%2Fac4968

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