Mass-losing Semiregular Variable Stars in Baade's Windows
Abstract
By cross-correlating the results of two recent large-scale surveys, the general properties of a well-defined sample of semiregular variable stars have been determined. ISOGAL mid-infrared photometry (7 and 15 μm) and MACHO V and R light curves are assembled for approximately 300 stars in the Baade's windows of low extinction toward the Galactic bulge. These stars are mainly giants of late M spectral type, evolving along the asymptotic giant branch (AGB). They are found to possess a wide and continuous distribution of pulsation periods and to obey an approximate logP-Mbol relation or set of such relations. Approximate mass-loss rates M in the range of ~1×10-8 to 5×10-7 Msolar yr-1 are derived from ISOGAL mid-infrared photometry and models of stellar spectra adjusted for the presence of optically thin circumstellar silicate dust. Mass-loss rates depend on luminosity and pulsation period. Some stars lose mass as rapidly as short-period Mira variables but do not show Mira-like amplitudes. A period of 70 days or longer is a necessary but not sufficient condition for mass loss to occur. For AGB stars in the mass-loss ranges that we observe, the functional dependence of mass-loss rate on temperature and luminosity can be expressed as M~TαLβ, where α=-8.80+0.96-0.24 and β=+1.74+0.16-0.24, in agreement with recent theoretical predictions. If we include our mass-loss rates with a sample of extreme mass-losing AGB stars in the Large Magellanic Cloud and ignore T as a variable, we get the general result for AGB stars that M~L2.7, valid for AGB stars with 10-8<M<10-4 Msolar yr-1.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2001
- DOI:
- 10.1086/320440
- arXiv:
- arXiv:astro-ph/0101094
- Bibcode:
- 2001ApJ...552..289A
- Keywords:
-
- Astronomical Data Bases: Miscellaneous;
- Galaxy: Bulge;
- Infrared: Stars;
- Stars: AGB and Post-AGB;
- Stars: Fundamental Parameters;
- Stars: Late-Type;
- Stars: Variables: Other;
- Astrophysics
- E-Print:
- to appear in The Astrophysical Journal, 51 pages, 9 figures, 3 tables