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Published May 1998 | Published + Submitted
Journal Article Open

The Luminosity Function and Initial Mass Function in the Galactic Bulge

Abstract

We present deep photometry obtained with the Hubble Space Telescope in a field in Baade's window in the Galactic bulge. We derive a luminosity function down to I ~ 24.3, or V ~ 27.5, corresponding to M ~ 0.3 M_☉. 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 ∝ M^(-2.2) for M ≳ 0.7 M_☉. However, we find strong evidence for a break in the mass function slope around 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 binary fraction and the accuracy of our completeness correction. This mass function should directly reflect the initial mass function.

Additional Information

© 1998. The American Astronomical Society. Received 1997 November 5; revised 1998 January 26. This work was supported in part by NASA under contract NAS 7-918 to JPL. We gratefully acknowledge I. Baraffe and F. Allard for communicating some of their stellar model and atmosphere results before publication. We thank the referee, A. Gould, for several very useful comments and suggestions.

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