MAGNITUDE OFFSET BETWEEN LENSED STARS AND OBSERVED STARS - A NEW PROBE OF THE STRUCTURE OF THE GALACTIC BAR

We propose a new method that can be used to constrain the properties o f the Galactic bar (bulge). If the majority of the lensing objects are in the Galactic bar, then we predict a systematic offset in the appar ent magnitude between lensed stars and all observed stars. Using OGLE color-magnitude diagram data we model this effect in the region of the diagram dominated by bulge red clump stars and find that for some mod els of the Galactic bar the expected offset in the apparent magnitude may be as large as 0.2 mag. About 100 lensed stars in the red clump re gion of the color-magnitude diagram are needed to unambiguously detect this effect, a number within the reach of current microlensing projec ts. We find a good correlation between the extent of the bar along the line of sight and the expected magnitude offset. We also obtain a con straint for the extent of the bar along the line of sight using the ob served luminosity function for the red clump stars.