Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003a%26a...405..341m&link_type=abstract
Astronomy and Astrophysics, v.405, p.341-348 (2003)
Astronomy and Astrophysics
Astrophysics
19
Stars: Planetary Systems, Infrared: Stars, Planets And Satellites: General
Scientific paper
Atmospheric models of the extrasolar, close-in giant planet HD 209458b predict strong absorption features from alkali metals (Seager & Sasselov \cite{Seager00}; Brown 2001). This was confirmed by the discovery of NaI by HST observations (Charbonneau et al. \cite{Charbonneau02}). In this study we focus on the search for the helium absorption feature at 10 830 Å, also predicted to be among the strongest ones. Helium is a major component of the planet's exosphere, for which models are yet not as robust as atmosphere models. One full transit was observed with the VLT/ISAAC instrument. We do not report the detection of the HeI feature. The data set is strongly affected by instrumental fringing, at a level up to 5% in the extracted spectra. After filtering, a residual noise of the order of 0.2% remains. An upper limit of the HeI line was derived, which further constrains future models of the HD 209458b planet exosphere. This upper limit, in terms of the feature depth, is 0.5% at 3sigma for a 3 Å bandwidth. Prospects are proposed to lower the detectability limit; the ultimate detectability limit with ISAAC in the absence of electronic fringing and in ideal atmospheric conditions could be as low as a line depth of 0.1% (3 Å width, 3sigma ).
Based on data acquired on the Very Large Telescope at Paranal Observatory, ESO Chile.
Coustenis Athena
Mayor Marcel
Moutou Claire
Queloz Didier
Schneider Jeff
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