Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sf2a.conf..253l&link_type=abstract
SF2A-2007: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics held in Grenoble, France, July
Astronomy and Astrophysics
Astrophysics
Scientific paper
The history of the mass loss experienced by stars on the Asymptotic Giant Branch (AGB) is a key issue for describing the late stages of evolution of low and intermediate mass (1 - 6 M&sun;) stars, as well as an important ingredient for the characterization of the cosmic cycle of matter. As the mass-loss rates of AGB stars are variable, it is difficult to establish a balance of the mass loss over the long periods of time that need to be considered (104 - 106 years). As hydrogen is the main constituent of the stellar wind, the HI line at 21 cm should be a useful tracer of circumstellar environments (CSEs) for stars with an effective temperature larger than 2500 K, in which case the hydrogen in the envelope is mostly atomic. Therefore HI emission could be a diagnostic probe of the late stages of stellar evolution. Y CVn is such an example and shows the strongest HI line to date. We can detect both the HI counterpart of the CO emission coming from the inner envelope and the HI counterpart of the IR emission in the outer envelope. The HI profile is composed of two features: a narrow (˜ 3 km.s-1) and strong one (˜400 mJy) that we associate with the latter and a faint (˜10 mJy), broad (˜ 15 km.s-1), rectangular one that we associate with the former. The high spectral resolution that can be obtained at λ = 21 cm allows to constrain the physical conditions in the CSEs.
Bertre Th. Le
Gerard Emmanuelle
Libert Yannick
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