Mass-losing semiregular variable stars in Baade's windows

C. Alard, J.A.D.L. Blommaert, C. Cesarsky, N. Epchtein, M. Felli, P. Fouque, S. Ganesh, R. Genzel, G. Gilmore, I.S. Glass, H. Habing, A. Omont, M. Perault, S. Price, A. Robin, M. Schultheis, G. Simon, J.T. Van Loon, C. Alcock, R.A. AllsmanD.R. Alves, T.S. Axelrod, A.C. Becker, D.P. Bennett, K.H. Cook, A.J. Drake, K.C. Freeman, M. Geha, K. Griest, M.J. Lehner, S.L. Marshall, D. Minniti, C. Nelson, B.A. Peterson, P. Popowski, M.R. Pratt, Peter Quinn, W. Sutherland, A.B. Tomaney, T. Vandehei, D.L. Welch

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    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 mum) 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 log P-M-bol relation or set of such relations. Approximate mass-loss rates (M) over dot in the range of similar to 1x10(-8) to 5 x 10(-7) M-. 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 AGE 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) over dot proportional to (TLbeta)-L-alpha, where a = -8.80(-0.24)(+0.96) and beta = + 1.74(-0.24)(+0.16), in agreement with recent theoretical predictions. If we include our mass-loss rates with a sample of extreme mass-losing AGE stars in the Large Magellanic Cloud and ignore T as a variable, we get the general result for AGE stars that (M) over dot proportional to L-2.7, valid for AGB stars with 10(-8) <(M) over dot ( 10(-4) M-. yr(-1).
    Original languageEnglish
    Pages (from-to)289-308
    JournalThe Astrophysical Journal
    Issue number1
    Publication statusPublished - 2001


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