M giants in Baade's window - Infrared colors, luminosities, and implications for the stellar content of E and S0 galaxies
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Abstract
Infrared JHKL, [10], CO, and H2O observations of 185 M1-9 giants in Baade's window are presented. The majority of these stars constitute an unbiased sample drawn from complete surveys for such stars. Information on bolometric luminosities, metallicity distribution functions, blanketing effects, mass loss and circumstellar emission is derived for nonvariable and long-period variable giants. On the whole, the observed characteristics of the bulge M giants are consistent with their being representatives of a population with a metallicity considerably in excess of solar. The luminosities of both the variables and nonvariables are consistent with an age comparable to that of Galactic globular clusters. Using the bulge M giants for the equivalent component of stellar synthesis models of galaxies results in infrared colors and indices which come close to but do not exactly match those of real galaxies. The remaining problem with the models is that stars other than M giants are not of sufficiently high metallicity. Increasing this metallicity results in a model that closely reproduces the energy distribution of E and S0 galaxies from 0.5 to 10 μm.