Borislav
Jovian
Number of posts : 564
Registration date : 2008-11-12
 | | Subject: Discovery of the second hydrogen exoplanet corona 12th March 2010, 7:06 am | |
| http://arxiv.org/abs/1003.2206 - Quote :
- Evaporation of the planet HD189733b observed in HI Lyman-alpha
We observed three transits of the extrasolar planet HD189733b in HI Lyman-alpha and in a few other lines in the ultraviolet with HST/ACS, in the search for atmospheric signatures. We detect a transit signature in the Lyman-alpha light curve with a transit depth of 5.05 +/- 0.75 %. This depth exceeds the occultation depth produced by the planetary disk alone at the 3.5-sigma level (statistical). Other stellar emission lines are less bright, and, taken individually, they do not show the transit signature, while the whole spectra redward of the Lyman-alpha line has enough photons to show a transit signature consistent with the absorption by the planetary disk alone. The transit depth's upper limits in the emission lines are 11.1% for OI at 1305A and 5.5% for CII at 1335A. The presence of an extended exosphere of atomic hydrogen around HD189733b producing 5% absorption of the full unresolved Lyman-alpha line flux shows that the planet is losing gas. The Lyman-alpha light curve is well-fitted by a numerical simulation of escaping hydrogen in which the planetary atoms are pushed by the stellar radiation pressure. We constrain the escape rate of atomic hydrogen to be between 10^9 and 10^{11} g/s and the ionizing extreme UV flux between 2 and 40 times the solar value (1-sigma), with larger escape rates corresponding to larger EUV flux. The best fit is obtained for dM/dt=10^{10} g/s and an EUV flux F_{EUV}=20 times the solar value. HD189733b is the second extrasolar planet for which atmospheric evaporation has been detected. | |
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Sirius_Alpha
Admin
Number of posts : 4320
Location : Earth
Registration date : 2008-04-06
| | Subject: Re: Discovery of the second hydrogen exoplanet corona 12th March 2010, 8:28 am | |
| Looks like it still needs confirmation. - Quote :
- In summary, we have presented the 3.5 sigma detection of an excess absorption in the Lyman-alpha transit light curve. ... Any detection at this level of confidence would call for an observational confirmation, which may be possible with the repaired STIS spectrograph. If confirmed, HD 189733 b would be the second extrasolar planet for which evaporation has been detected.
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