Low mass loss in late type stars

Details Low mass loss in late type stars Low mass loss in late type stars

Feb 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003esasp.511..145r&link_type=abstract

Exploiting the ISO Data Archive. Infrared Astronomy in the Internet Age, held in Siguenza, Spain 24-27 June, 2002. Edited by

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The spectra of 83 giant stars obtained by the ISO/SWS covering the wavelength range 2.4 - 45 μm have been analysed. The stars of our sample have been selected on the basis of their IRAS colors as low mass loss candidates ([12]-[25] < 0 and [25]-[60] < -1.8, where [12]-[25] = 2.5;log(F25/F12) and [25]-[60] = 2.5;log(F60/F25)). The sample includes 10 supergiants, 30 Miras, 27 Semiregular Variables (SRVs) , 5 irregulars (IRVs) and 12 IRAS objects of different types, all these stars are surrounded by oxygen-rich dust shells characterized by silicate emission.
The spectra are analysed in terms of a spherical radiative transfer model based on the DUSTY code. The model fits to the SED restricted to the ISO/SWS wavelength range allow us to evaluate reasonably well the optical depth at 10 μm, especially since the present study is a differential analysis of the mass loss versus variability properties for stars with small mass-loss rates. In addition, taking into account the spectral type of the star, the presence of 10 and 18 μm silicate emission features constrains drastically the other model fit parameters. The optical depth at 10 μm spans the range 0.01 to 1.8 for all the stars of our sample, with the upper limit corresponding in fact to the value where in average the 10 μm dust feature shows in self absorption and translates to a dust mass loss rate M&sun;d around 10-7 M&sun;y-1 for an optically visible Mira whose luminosity equals 104 L&sun;. The optical depth distribution peaks abruptly around 0.05 both for Miras and SRVs, whereas supergiants are apparently more uniformly distributed in the full range. Almost all our stars have HIPPARCOS derived distances so an accurate determination of mass loss rates will be made.
The ISO/SWS spectra are compared to their equivalent IRAS/LRS in order to account for variability of the SED in the near and mid-infrared and to check for long-term changes of the circumstellar material surrounding these stars.

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