We present deep photometry obtained with the Hubble Space Telescope ( HST ) in a field in Baade ’ s Window in the Galactic bulge .
We derive a luminosity function down to I \sim 24.3 , or V \sim 27.5 , corresponding to M \sim 0.3 M _ { \odot } .
The luminosity function from the turnoff down to this level appears remarkably similar to that observed in the solar neighborhood .
We derive a mass function using both an empirical local mass-luminosity relation and a mass-luminosity relation from recent stellar model calculations , allowing for the presence of binaries and photometric errors .
The mass function has a power law form with dN / dM \propto M ^ { -2.2 } for M \mathrel { \vbox { \offinterlineskip \hbox { $ > $ } \kern 1.29 pt \hbox { $ \sim$ } } } 0.7 M _ { \odot } .
However , we find strong evidence for a break in the mass function slope around 0.5-0.7 M _ { \odot } , with a significantly shallower slope at lower masses .
The value of the slope for the low masses depends on the assumed binary fraction and the accuracy of our completeness correction .
This mass function should directly reflect the initial mass function .