Search for spectroscopical signatures of transiting HD 209458b's exosphere^*

¹ ESO, Alonso de Cordova 3107, Santiago de Chile e-mail: akaufer@eso.org
² Observatoire de Paris Meudon, 92195 Meudon Cedex, France e-mail: Athena.Coustenis@obspm.fr, Jean.Schneider@obspm.fr, Richard.Saint-Gilles@obspm.fr
³ Observatoire de Genève, Switzerland e-mail: michel.mayor@obs.unige.ch, didier.queloz@obs.unige.ch

Corresponding author: C. Moutou, cmoutou@eso.org

Received: 13 November 2000
Accepted: 18 January 2001

Abstract

Following recent attempts to detect the exosphere of the extra-solar planet 51 Pegb in the infrared (Coustenis et al. [CITE], [CITE]; Rauer et al. [CITE]), we discuss here a search for optical spectroscopic signatures from a gaseous extended envelope (called exosphere) surrounding the planet HD 209458b. This planet has a demonstrated photometric transit (Charbonneau et al. [CITE]; Henry et al. [CITE]), thus offering an increased probability for the spectroscopic detection of such an envelope. Therefore it is the best known candidate for probing the exospheric composition of a giant planet, orbiting a Sun-like star at a short distance. The observations were performed with UVES at the VLT and cover most of the 328-669 nm range. We did not detect HD 209458b's exosphere at a level of 1% , a value close to the predictions. We discuss here the first results obtained and their limitations, as well as future prospective.