AAS 195th Meeting, January 2000
Session 75. Intrinsic Variable Stars
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

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[75.06] Mass-Losing Semiregular Variable Stars in Baade's Windows

D. R. Alves (STScI), I. S. Glass (SAAO), MACHO and ISOGAL Collaborations

MACHO Project V and R lightcurves and ISOGAL mid-infrared photometry (7 and 15 microns) are assembled for approximately 300 stars in Baade's Windows of low extinction towards the Galactic Bulge. These stars are primarily mass-losing giants of late M spectral type, and evolving along the asymptotic giant branch. The 7 micron flux from a late-type star with an optically thin, circumstellar dust shell arises from its photosphere, while the 15 micron flux is due to a combination of the photosphere and the dust. A tentative calibration of the ISOGAL photometry suggests that the stars in our sample exhibit a range of mass-loss rates from 10-7 to 10-9 solar masses per year. Using the MACHO lightcurves, we classify the majority of these stars as semiregular variables.

This is the first large sample of semiregular variable stars whose pulsation and mass-loss rates are well-characterized, and whose distances, and thus energetics, are also known. In this preliminary report, we describe our search for periodic variability using the MACHO lightcurves. We find that luminosity, mass-loss rate, and pulsation period are correlated, in the sense that semiregulars with higher luminosities and higher mass-loss rates have longer periods. We note that this work is an example of data-mining in two large astronomical survey databases, which may become more common this century.

This research was partially supported by a grant from NASA administered by the American Astronomical Society.

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