ISOGAL survey of Baade's Windows

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The Baade's Windows of low obscuration towards the inner parts of the Galactic bulge represent ideal places in which to develop an understanding of the ISOGAL colour-magnitude diagrams. Unlike the case for the solar neighbourhood, their contents are at a uniform distance from the Sun, affected only by the finite thickness of the Bulge. The objects detected in the ISOGAL survey are found to be late-type M-giants at the red giant tip or on the Asymptotic Giant Branch (AGB). The ISOGAL colour-magnitude diagrams show that mass-loss starts at about M4 and increases towards later types. Many non-Miras have mass-loss rates similar to shorter-period Miras. The visible counterparts of the ISOGAL sources have been identified in the database of the MACHO gravitational lensing survey. A first report of this work is included here. It is found that nearly all the ISOGAL sources are semi-regular variables (SRVs), which are many times more numerous than Miras. Their stellar luminosities increase with period. Based on a simple interpretation of the photometry, mass-loss rates from about 10⁻⁹ to 10⁻⁷ solar masses per year are found for SRVs with periods in excess of about days.