2000A&A...357..515B

The distances and the mass-loss rates of carbon stars are in general very poorly known. The various estimates of the distances, taken from the general literature, show considerable discrepancies, while the evaluations of the mass-loss rates can be in error by more than an order of magnitude. In this work we have evaluated these two important stellar parameters for a previously selected sample of 55 carbon stars showing the 11.3 µm band, commonly attributed to silicon carbide (SiC) grains. To perform the calculation we have used the values of geometrical and physical parameters of these sources obtained from the best fits of their observed spectra. Using the distance values derived in this way and the 11.3 µm band intensity, we have evaluated the absolute band strength and we have found that, in agreement with other authors, there is a correlation between this quantity and the mass-loss rate. This correlation can be very useful to determine the mass-loss rate of other carbon stars not included in our sample, by means of the intensity of the SiC band, without using the usual technique based on CO observations. The same procedure can be conveniently applied to the same as well as to other carbon stars, whose spectra will be available to the community in the next future (i.e. the infrared spectra of sources observed by the Infrared Satellite Observatory, ISO).