The Peculiar Atmospheric Chemistry of KELT-9b

Kitzmann, Daniel; Heng, Kevin; Rimmer, Paul B.; Hoeijmakers, Jens; Tsai, Shang-Min; Malik, Matej; Lendl, Monika; Deitrick, Russell John; Demory, Brice-Olivier (2018). The Peculiar Atmospheric Chemistry of KELT-9b. Astrophysical journal, 863(2), p. 183. Institute of Physics Publishing IOP 10.3847/1538-4357/aace5a

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The atmospheric temperatures of the ultra-hot Jupiter KELT-9b straddle the transition between gas giants and stars, and therefore between two traditionally distinct regimes of atmospheric chemistry. Previous theoretical studies assume the atmosphere of KELT-9b to be in chemical equilibrium. Despite the high ultraviolet flux from KELT-9, we show using photochemical kinetic calculations that the observable atmosphere of KELT-9b is predicted to be close to chemical equilibrium, which greatly simplifies any theoretical interpretation of its spectra. It also makes the atmosphere of KELT-9b, which is expected to be cloud-free, a tightly constrained chemical system that lends itself to a clean set of theoretical predictions. Due to the lower pressures probed in transmission (compared to emission) spectroscopy, we predict the abundance of water to vary by several orders of magnitude across the atmospheric limb depending on temperature, which makes water a sensitive thermometer. Carbon monoxide is predicted to be the dominant molecule under a wide range of scenarios, rendering it a robust diagnostic of the metallicity when analyzed in tandem with water. All of the other usual suspects (acetylene, ammonia, carbon dioxide, hydrogen cyanide, methane) are predicted to be subdominant at solar metallicity, while atomic oxygen, iron, and magnesium are predicted to have relative abundances as high as 1 part in 10,000. Neutral atomic iron is predicted to be seen through a forest of optical and near-infrared lines, which makes KELT-9b suitable for high-resolution ground-based spectroscopy with HARPS-N or CARMENES. We summarize future observational prospects of characterizing the atmosphere of KELT-9b.

Item Type:

Journal Article (Original Article)

Division/Institute:

10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute > NCCR PlanetS
08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute

UniBE Contributor:

Kitzmann, Daniel; Heng, Kevin; Hoeijmakers, Jens; Tsai, Shang-Min; Malik, Matej; Deitrick, Russell John and Demory, Brice-Olivier

Subjects:

500 Science > 520 Astronomy
500 Science > 530 Physics

ISSN:

0004-637X

Publisher:

Institute of Physics Publishing IOP

Language:

English

Submitter:

Danielle Zemp

Date Deposited:

03 Jun 2019 16:29

Last Modified:

03 Jun 2019 16:29

Publisher DOI:

10.3847/1538-4357/aace5a

BORIS DOI:

10.7892/boris.126844

URI:

https://boris.unibe.ch/id/eprint/126844

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