Strong H2O and CO Emission Features in the Spectrum of KELT-20b Driven by Stellar UV Irradiation
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 ~ 2200 K 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 0.6-4.5 μm with data from TESS, HST WFC3/G141, and Spitzer 4.5 μm channel. KELT-20b has a 1.4 μm water feature strength metric of ${{\rm{S}}}_{{{\rm{H}}}_{2}{\rm{O}}}$ SH2O = -0.097 ± 0.02 and a blackbody brightness temperature difference of 528 K between WFC3/G141 (T b = 2402 ± 14 K) and Spitzer 4.5 μm channel (T b = 2930 ± 59 K). These very large H2O 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 (Teff = 8720 ± 250 K) is expected to be the key that drives its strong thermal inversion and prominent emission features based on previous PHOENIX model calculations.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2022
- DOI:
- arXiv:
- arXiv:2201.02261
- Bibcode:
- 2022ApJ...925L...3F
- Keywords:
-
- 487;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 9 pages, 3 figures, 1 table, accepted to ApJL
