High-resolution detection of neutral oxygen and non-LTE effects in the atmosphere of KELT-9b
Abstract
Oxygen is a constituent of many of the most abundant molecules detected in exoplanetary atmospheres and a key ingredient for tracking how and where a planet formed1. In particular, the O I 777.4 nm triplet is used to probe airglow and aurora on the Earth2 and the oxygen abundance in stellar atmospheres3-6, but has not been detected in an exoplanet atmosphere before. We present a definite ground-based detection of the neutral oxygen 777.4 nm triplet lines in the transmission spectrum of the ultrahot Jupiter KELT-9b7, the hottest known giant planet. The synthetic spectrum computed employing novel non-local thermodynamic equilibrium radiative transfer calculations8 matches the data significantly better than that computed assuming local thermodynamic equilibrium. These non-local thermodynamic equilibrium radiative transfer calculations imply a mass-loss rate of 108-109 kg s−1, which exceeds the lower limit of 107-108 kg s−1 required to facilitate the escape of oxygen and iron from the atmosphere. Assuming a solar oxygen abundance, the non-local thermodynamic equilibrium model points towards the need for microturbulence and macroturbulence broadening of 3.0 ± 0.7 km s−1 and 13 ± 5 km s−1, respectively, indicative of the presence of fast winds in the middle and upper atmosphere. Present and upcoming high-resolution spectrographs will allow the detection in other exoplanets of the 777.4 nm O I triplet, which is a powerful tool to constrain the key characteristics of exoplanetary atmospheres when coupled with forward modelling accounting for non-local thermodynamic equilibrium effects.
- Publication:
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Nature Astronomy
- Pub Date:
- December 2021
- DOI:
- 10.1038/s41550-021-01544-4
- arXiv:
- arXiv:2112.12059
- Bibcode:
- 2022NatAs...6..226B
- Keywords:
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- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- Authors' version of an article published in Nature Astronomy on 22 Dec 2021. Link to the paper: https://rdcu.be/cDHW1