On the extinction towards Baade's Window

Abstract

An analysis is made on the morphology of the sequences, formed by stars distributed along the line of sight in (V,V--I) colour-magnitude diagrams from Baade's Window (l=1.0,b=-3.9). The extinction is due to an absorbing layer with an effective thickness of about 100 pc. A linearly, with distance, increasing extinction up to a maximum value inside the absorbing layer is in first order a good approximation for the actual extinction present along the line of sight. We show that the morphology of the disc sequence gives a good indication of the nearby extinction along the line of sight. The morphology of the bulge/bar red horizontal branch is likely due to a combination of differential reddening and a significant metallicity spread among the horizontal branch stars. This is irrespective of the type of extinction law adopted. There is in Baade's Window globally no big difference between a Poissonian or a patchy type of extinction, except for substructures in the morphology of the sequences for the latter.