Spectroscopy of New High Proper Motion Stars in the Northern Sky. I. New Nearby Stars, New High-Velocity Stars, and an Enhanced Classification Scheme for M Dwarfs

We define an enhanced spectral classification scheme for M dwarf stars, anduse it to derive spectral classification of 104 northern stars with propermotions larger than 0.5"/yr which we discovered in a survey of high propermotion stars at low galactic latitudes. The final tally is as follows: 54 Mdwarfs, 25 sdK and sdM subdwarfs, 14 esdK and esdM extreme subdwarfs, and 11 DAand DC white dwarfs. Among the most interesting cases, we find one star to bethe coolest subdwarf ever reported (LSR2036+5059, with spectral type sdM7.5), anew M9.0 dwarf only about 6pc distant (LSR1835+3259), and a new M6.5 dwarf only7pc from the Sun (LSR2124+4003). Spectroscopic distances suggests that 27 ofthe M dwarfs, 3 of the white dwarfs, and one of the subdwarfs (LSR2036+5059)are within 25pc of the Sun, making them excellent candidates for inclusion inthe solar neighborhood census. Estimated sky-projected velocities suggest thatmost of our subdwarfs and extreme subdwarfs have halo kinematics. We find thatseveral white dwarfs and non metal-poor M dwarfs also have kinematicsconsistent with the halo, and we briefly discuss their possible origin.Comment: 53 pages, 18 figures, 5 tables, accepted by The Astronomical Journal; this updated version includes radial velocities for the stars and an expanded discussio