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Issue A&A
Volume 454, Number 2, August I 2006
APEX Special Booklet
Page(s) L103 - L106
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20065285



A&A 454, L103-L106 (2006)
DOI: 10.1051/0004-6361:20065285

Letter

Mass-loss properties of S-stars on the AGB

S. Ramstedt1, F. L. Schöier1, H. Olofsson1, 2 and A. A. Lundgren3

1  Stockholm Observatory, AlbaNova University Center, 106 91 Stockholm, Sweden
    e-mail: sofia@astro.su.se
2  Onsala Space Observatory, 439 92 Onsala, Sweden
3  European Southern Observatory, Casilla 19001, Santiago 19, Chile

(Received 27 March 2006 / Accepted 12 May 2006 )

Abstract
We have used a detailed non-LTE radiative transfer code to model new APEX CO(J = 3  $\rightarrow$ 2) data, and existing CO radio line data, on a sample of 40 AGB S-stars. The derived mass-loss-rate distribution has a median value of 2 $\times$ 10 $^{-7}~M_{\odot}$ yr-1, and resembles values obtained for similar samples of M-stars and carbon stars. Possibly, there is a scarcity of high-mass-loss-rate ($\ge$10 $^{-5}~M_{\odot}$ yr-1) S-stars. The distribution of envelope gas expansion velocities is similar to that of the M-stars, the median is 7.5 km s-1, while the carbon stars, in general, have higher gas expansion velocities. The mass-loss rate correlates well with the gas expansion velocity, in accordance with results for M-stars and carbon stars.


Key words: stars: AGB and post-AGB -- stars: circumstellar matter -- stars: late-type -- stars: mass-loss



© ESO 2006


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