New study of the line profiles of sodium perturbed by H₂^⋆

¹ GEPI, Observatoire de Paris, PSL Research University, UMR 8111, CNRS, Sorbonne Paris Cité, 61, Avenue de l’Observatoire, 75014 Paris, France
e-mail: nicole.allard@obspm.fr
² Institut d’Astrophysique de Paris, UMR7095, CNRS, Université Paris VI, 98bis Boulevard Arago, Paris, France
³ Laboratoire de Physique et de Chimie Quantique, Université de Toulouse (UPS) and CNRS, 118 route de Narbonne, 31400 Toulouse, France
⁴ Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands

Received: 1 April 2019
Accepted: 2 July 2019

Abstract

The opacity of alkali atoms, most importantly of Na and K, plays a crucial role in the atmospheres of brown dwarfs and exoplanets. We present a comprehensive study of Na–H₂ collisional profiles at temperatures from 500 to 3000 K, the temperatures prevailing in the atmosphere of brown dwarfs and Jupiter-mass planets. The relevant H₂ perturber densities reach several 10¹⁹ cm⁻³ in hot (T_eff ≳ 1500 K) Jupiter-mass planets and can exceed 10²⁰ cm⁻³ for more massive or cooler objects. Accurate pressure-broadened profiles that are valid at high densities of H₂ should be incorporated into spectral models. Unified profiles of sodium perturbed by molecular hydrogen were calculated in the semi-classical approach using up-to-date molecular data. New Na–H₂ collisional profiles and their effects on the synthetic spectra of brown dwarfs and hot Jupiters computed with petitCODE are presented.