2006/01/01 by E. Gérard, T. Le Bertre, T. Le Bertre · 2 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #Astro and Planetary Science
paper · pdf · doi:10.1086/508811
We present new results of a spectroscopic survey of circumstellar Hi in the direction of evolved stars made with the Nançay Radiotelescope. The Hi line at 21 cm has been detected in the circumstellar shells of a variety of evolved stars: AGB stars, oxygen-rich and carbon-rich, Semi-Regular and Miras, and Planetary Nebulae. The emissions are generally spatially resolved, i.e. larger than 4 ′ , indicating shell sizes of the order of 1 pc which opens the possibility to trace the history of mass loss over the past ∼ 10 4 − 10 5 years. The lineprofiles are sometimes composite. The individual components have generally a quasi-Gaussian shape; in particular they seldom show the double-horn profile that would be expected from the spatially resolved optically thin emission of a uniformly expanding shell. This probably implies that the expansion velocity decreases outwards in the external shells (0.1–1 pc) of these evolved stars. The Hi line-profiles do not necessarily match those of the CO rotational lines. Furthermore, the centroid velocities do not always agree with those measured in