Astronomy and Astrophysics, volume 474, 301-306 (2007/10-4)
A method to detect H2 in the atmosphere of transiting extrasolar planets using the EUV spectrum.
BARTHELEMY M., LILENSTEN J. and PARKINSON C.D.
Abstract (from CDS):
We present a method to detect the molecular hydrogen in extrasolar planetary atmospheres. We model the coupling between H-Lyman lines and H2 lines due to wavelength overlapping between these lines. We also explore the overlapping between other stellar EUV lines especially the CIII line at 977.02Å and planetary H2 lines. If the spectrum of the planet is resolved, we show that H2 modifies the intensity and shape of the H-Lyman lines emitted by the planet. However, if observed in absorption spectroscopy during a transit, the modification of the stellar lines in the Lyman series by the atmospheric H2 is too low to be detectable with the current observing facilities. On the contrary, for HD209458b with a 25000km thick H2 layer, the intensity of the stellar CIII line at 977.02Å decreases by 2.64% during the transit. In the case of the newly discovered planet HD189733b, the decrease of the intensity of the CIII line reaches 3.78%. Such decreases could be detectable with a FUSE observation of several transits thereby constituting a way to detect H2 in exoplanetary atmospheres.
radiative transfer - stars: planetary systems - molecular processes - ultraviolet: general