A&A 429, 235-246 (2005)
DOI: 10.1051/0004-6361:20041280

The mass loss of C-rich giants

J. Bergeat and L. Chevallier

Centre de Recherche Astronomique de Lyon (UMR 5574 du CNRS), Observatoire de Lyon, 9 avenue Charles André, 69561 St-Genis-Laval Cedex, France
    e-mail: bergeat@obs.univ-lyon1.fr

(Received 12 May 2004 / Accepted 23 July 2004)

Abstract
The mass loss rates, expansion velocities and dust-to-gas density ratios from millimetric observations of 119 carbon-rich giants are compared, as functions of stellar parameters, to the predictions of recent hydrodynamical models. Distances and luminosities previously estimated from HIPPARCOS data, masses from pulsations and C/O abundance ratios from spectroscopy, and effective temperatures from a new homogeneous scale, are used. Predicted and observed mass loss rates agree fairly well, as functions of effective temperature. The signature of the mass range of most carbon-rich AGB stars is seen as a flat portion in the diagram of mass loss rate vs. effective temperature. It is flanked by two regions of mass loss rates increasing with decreasing effective temperature at nearly constant stellar mass. Four stars with detached shells, i.e. episodic strong mass loss, and five cool infrared carbon-rich stars with optically-thick dust shells, have mass loss rates much larger than predicted values. The latter (including CW Leo) could be stars of smaller masses ( ) while is indicated for most of the coolest objects. Among the carbon stars with detached shells, R Scl returned to a predicted level (16 times lower) according to recent measurements of the central source. The observed expansion velocities are in agreement with the predicted velocities at infinity in a diagram of velocities vs. effective temperature, provided the carbon to oxygen abundance ratio is i.e. the range deduced from spectra and model atmospheres of those cool variables. Five stars with detached shells display expansion velocities about twice that predicted at their effective temperature. Miras and non-Miras do populate the same locus in both diagrams at the present accuracy. The predicted dust-to-gas density ratios are however about 2.2 times smaller than the values estimated from observations. Recent drift models can contribute to minimize the discrepancy since they include more dust. Simple approximate formulae are proposed.

Key words: stars: AGB and post-AGB -- stars: carbon -- stars: mass-loss -- stars: variables: general

SIMBAD Objects
Tables at the CDS

© ESO 2004

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.