M Subdwarfs: The Population II Luminosity Function

We present results of a study of very low mass halo stars. Using a sample ofproper motion stars identified from plate material taken as part of the firstand second Palomar Sky Surveys, we measure the space density, metallicitydistribution, and kinematics of the Population II M subdwarfs. Our overallluminosity function is in good agreement with previous analyses of the spacedensity of nearby very-low-mass halo subdwarfs, and confirms the discrepancybetween local analyses and the space densities inferred from deep HSTstarcounts. We show for the first time that both the metallicity distributionand kinematics of late-type halo subdwarfs are consistent with those of theirhigher mass metal-poor counterparts. Dividing our sample by abundance, we findno evidence that the mass function of field halo stars is dependent uponmetallicity. We provide data for three nearby subdwarfs that may meritadditional observations.Comment: 34 pages inc. 10 figures. To appear in January 1999 Astronomical Journa