THE LUMINOSITY FUNCTION AND INITIAL MASS FUNCTION IN THE GALACTIC BULGE

We present deep photometry obtained with the Hubble Space Telescope in a held in Baade's window in the Galactic bulge, We derive a luminosit y function down to I similar to 24.3, or V similar to 27.5, correspond ing to M similar to 0.3 M.. The luminosity function from the turnoff d own to this level appears remarkably similar to that observed in the s olar neighborhood. We derive a mass function using both an empirical l ocal mass-luminosity relation and a mass-luminosity relation from rece nt stellar model calculations, allowing for the presence of binaries a nd photometric errors. The mass function has a power-law form with dN/ dM proportional to M-2.2 for M greater than or similar to 0.7 M.. Howe ver, we find strong evidence for a break in the mass function slope ar ound 0.5-0.7 M., with a significantly shallower slope at lower masses. The value of the slope for the low masses depends on the assumed bina ry fraction and the accuracy of our completeness correction. This mass function should directly reflect the initial mass function.