Research Note

The Mg i line: a new probe of the atmospheres of evaporating exoplanets

¹ CNRS, UMR 7095, Institut d’astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
e-mail: bourrier@iap.fr
² UPMC Univ. Paris 6, UMR 7095, Institut d’Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
³ Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland

Received: 17 December 2013
Accepted: 22 October 2014

Abstract

Transit observations of HD 209458b in the UV revealed signatures of neutral magnesium escaping the planet’s upper atmosphere. The absorption detected in the Mg i line provides unprecedented information on the physical conditions at the altitude where the atmospheric blow-off takes place. Here we use a 3D model of atmospheric escape to estimate the transit absorption signatures in the Mg i line of their host stars. The detectability of these signatures depends on the brightness of the star and the escape rate of neutral magnesium. We identify a sample of potentially evaporating exoplanets that covers a wide range of stellar and planetary properties, and whose extended exospheres might be detected through Mg i line observations with current UV facilities, allowing further steps in comparative exoplanetology.