No hydrogen exosphere detected around the super-Earth HD 97658 b
- V. Bourrier
- D. Ehrenreich
- G. King
- A. Lecavelier des Etangs
- P. J. Wheatley
- A. Vidal-Madjar
- F. Pepe
- S. Udry
DOIAbstract
The exoplanet HD 97658 b provides a rare opportunity to probe the atmospheric composition and evolution of moderately irradiated super-Earths. It transits a bright K star at a moderate orbital distance of 0.08 au. Its low density is compatible with a massive steam envelope that could photodissociate at high altitudes and become observable as escaping neutral hydrogen. Our analysis of three transits with HST/STIS at Lyman-α reveals no such signature, suggesting that the thermosphere of HD 97658 b is not hydrodynamically expanding and is subjected to a low escape of neutral hydrogen (<108 g s-1 at 3σ). Using HST/STIS Lyman-α observations and Chandra/ACIS-S and XMM-Newton/EPIC X-ray observations at different epochs, we find that HD 97658 is in...
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