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 and use it to derive spectral classification of 104 northern stars with proper motions larger than 0.5 yr(-1) that we discovered in a survey of high proper motion stars at low Galactic latitudes. The final tally is as follows: 54 M dwarfs, 25 sdK and sdM subdwarfs, 14 esdK and esdM extreme subdwarfs, and 11 DA and DC white dwarfs. Among the most interesting cases, we find one star to be the coolest subdwarf ever reported (LSR 2036+ 5059, with spectral type sdM7.5), a new M9.0 dwarf only about 6 pc distant ( LSR 1835+3259), and a new M6.5 dwarf only 7 pc from the Sun ( LSR 2124+4003). Spectroscopic distances suggests that 27 of the M dwarfs, three of the white dwarfs, and one of the subdwarfs (LSR 2036+ 5059) are within 25 pc of the Sun, making them excellent candidates for inclusion in the solar neighborhood census. Estimated sky-projected velocities suggest that most of our subdwarfs and extreme subdwarfs have halo kinematics. We find that several white dwarfs and non metal-poor M dwarfs also have kinematics consistent with the halo, and we briefly discuss their possible origin.