High-resolution detection of neutral oxygen and non-LTE effects in the atmosphere of KELT-9b

DOI: 
10.1038/s41550-021-01544-4
Publication date: 
01/02/2022
Main author: 
Borsa, Francesco
IAA authors: 
Shulyak, Denis
Authors: 
Borsa, Francesco;Fossati, Luca;Koskinen, Tommi;Young, Mitchell E.;Shulyak, Denis
Journal: 
Nature Astronomy
Publication type: 
Article
Volume: 
6
Pages: 
226-231
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 formed<SUP>1</SUP>. In particular, the O I 777.4 nm triplet is used to probe airglow and aurora on the Earth<SUP>2</SUP> and the oxygen abundance in stellar atmospheres<SUP>3-6</SUP>, 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-9b<SUP>7</SUP>, the hottest known giant planet. The synthetic spectrum computed employing novel non-local thermodynamic equilibrium radiative transfer calculations<SUP>8</SUP> 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 10<SUP>8</SUP>-10<SUP>9</SUP> kg s<SUP>−1</SUP>, which exceeds the lower limit of 10<SUP>7</SUP>-10<SUP>8</SUP> kg s<SUP>−1</SUP> 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<SUP>−1</SUP> and 13 ± 5 km s<SUP>−1</SUP>, 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.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2021NatAs.tmp..253B/abstract
ADS Bibcode: 
2021NatAs.tmp..253B
Keywords: 
Astrophysics - Earth and Planetary Astrophysics