Mass-losing AGB stars: infrared observations and evolutionary implications
Abstract
We have selected a wide database of mid-infrared observations, for AGB stars from both ground-based and space-borne observatories, with the aim of characterizing the efficient mass loss mechanisms that lead to the formation of their extended dusty envelopes. Our sample includes more than 400 sources in our Galaxy, distributed along the evolutionary sequence that gradually changes the spectral characteristics of M giants to MS, S and then C-stars. Thanks to a reanalysis of existing estimates of mass loss at radio frequencies and to improved measurements of distance (often provided by the Hipparcos mission), we compile a homogeneous set of corrected mass-loss rates and of near and mid-infrared colours. We show the existence of clear correlations. This suggests that mass loss can be inferred from photometric colours in mid-infrared, once these have been suitably calibrated. This provides a tool to predict the efficiency of stellar winds for other less known sources and is a decisive step in view of the determination of observationally based criteria for inclusion of mass loss in stellar models. In this paper we discuss in particular our sample of C-rich stars.
- Publication:
-
Memorie della Societa Astronomica Italiana
- Pub Date:
- 2004
- Bibcode:
- 2004MmSAI..75..617G
- Keywords:
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- Stars: AGB and post-AGB;
- Mass Loss;
- Carbon Stars;
- Infrared Photometry