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We derive mass functions (MF) for halo red dwarfs (the faintest hydrogenburning stars) and then extrapolate to place limits on the total mass of halobrown dwarfs (stars not quite massive enough to burn hydrogen). The massfunctions are obtained from the luminosity function of a sample of 114 localhalo stars in the USNO parallax survey (Dahn \etal 1995). We use stellar modelsof Alexander \etal (1996) and make varying assumptions about metallicity andabout possible unresolved binaries in the sample. We find that the MF for halored dwarfs cannot rise more quickly than $1/m^2$ as one approaches the hydrogenburning limit. Using recent results from star formation theory, we extrapolatethe MF into the brown-dwarf regime. We see that likely extrapolations implythat the total mass of brown dwarfs in the halo is less than $\sim 3\%$ of thelocal mass density of the halo ($\sim 0.3\%$ for the more realistic models weconsider). Our limits apply to brown dwarfs in the halo that come from the samestellar population as the red dwarfs.Comment: Significant changes over previous submission. To be published ApJ  Letters, 16 pages, latex, one figur

The Mass Function of Low-Mass Halo Stars: Limits on Baryonic Halo Dark Matter