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A. Gould, S. Salim (Ohio State University)
Luyten's NLTT catalog lists 59,000 stars with proper motions greater than 0.2 arcsec/yr, making it an excellent source of candidate M dwarfs, white dwarfs, and halo subdwarfs. However, NLTT has only crude positions and very approximate photographic magnitudes. Just a small fraction of these stars have precise multicolor photometry, spectroscopy or trigonometric parallaxes from other sources, a shortcoming that renders ambiguous even basic classification. We overcome these limitations by locating counterparts to NLTT stars in wide-area sky surveys: USNO-A, 2MASS, and SDSS. Precise near-IR and optical photometry, and refined astrometry, allow us to explore the properties of high proper motion stars with greater accuracy. Thus we are able, using the reduced proper motion, to classify NLTT stars with significantly improved certainty, as belonging to white dwarf, subdwarf or main sequence dwarf populations. SDSS u*-band photometry of NLTT stars yields approximate metallicity information on subdwarfs, allowing us to statistically characterize the kinematics of subdwarfs of different metallicities, or conversely, about the subdwarf color-magnitude relation. We also explore the distribution of white dwarf motions, with emphasis on high velocities.