ISOGAL survey of Baade's Windows

Abstract

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.