학술논문
Mass-Losing Semiregular Variable Stars in Baade's Windows
Document Type
Working Paper
Author
Alard, C.; Blommaert, J.; Cesarsky, C.; Epchtein, N.; Felli, M.; Fouque, P.; Ganesh, S.; Genzel, R.; Gilmore, G.; Glass, I.; Habing, H.; Omont, A.; Perault, M.; Price, S.; Robin, A.; Schultheis, M.; Simon, G.; van Loon, J.; Alcock, C.; Allsman, R.; Alves, D.; Axelrod, T.; Becker, A.; Bennett, D.; Cook, K.; Drake, A.; Freeman, K.; Geha, M.; Griest, K.; Lehner, M.; Marshall, S.; Minniti, D.; Nelson, C.; Peterson, B.; Popowski, P.; Pratt, M.; Quinn, P.; Sutherland, W.; Tomaney, A.; Vandehei, T.; Welch, D.
Source
Subject
Language
Abstract
By cross-correlating the results of two recent large-scale surveys, the general properties of a well defined sample of semi-regular variable stars have been determined. ISOGAL mid-infrared photometry and MACHO lightcurves are assembled for approximately 300 stars in the Baade's Windows of low extinction towards 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 log~period -- bolometric magnitude relation or set of such relations. Approximate mass-loss rates in the range of 1e-8 to 5e-7 M_sun per year 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 Miras but do not show Mira-like amplitudes. A period of 70 days or longer is a necessary but not a 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 is found to be 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, we get the general result for AGB stars that mass-loss rate is proportional to luminosity^{2.7}, valid for AGB stars with 10^{-8} to 10^{-4} M_sun per year (Abridged).
Comment: to appear in The Astrophysical Journal, 51 pages, 9 figures, 3 tables; table 1 will be available in machine-readable format at the electronic ApJ
Comment: to appear in The Astrophysical Journal, 51 pages, 9 figures, 3 tables; table 1 will be available in machine-readable format at the electronic ApJ