We show that faint red stars do not contribute significantly to the mass budget of the Galaxy or to microlensing statistics. Our results are obtained by analyzing two long exposures of a high-latitude field taken with the Wide Field Camera on the newly repaired { \it Hubble Space Telescope}. Stars are easily distinguished from galaxies essentially to the limiting magnitudes of the images. We find five stars with $2.0<V-I<3.0$ and $I<25.3$ and no stars with $V-I>3.0$. Therefore, main-sequence stars with $M_I>10$ that are above the hydrogen-burning limit in the dark halo or the spheroid contribute $<6%$ of the unseen matter. Faint red disk stars, M-dwarfs, contribute at most $ 15%$ to the mass of the disk. We parameterize the faint end of the cumulative distribution of stars, $\Phi$, as a function of luminosity $L_V$, $d\Phi/d \ln L_V \propto L_V^{ -\gamma}$. For spheroid stars, $\gamma<0.32$ over the range $6<M_V<17$, with 98% confidence. The disk luminosity function falls, $\gamma<0$, for $15\lsim M_V\lsim 19$. Faint red stars in the disk or thick disk, and stars with $M_V<16$ in the spheroid contribute $\tau< 10^{ -8}$ to the optical depth to microlensing toward the Large Magellanic Cloud.
Categories: astro-ph