The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics

Abstract

The Third Catalogue of Nearby Stars (Gliese & Jahreiss Preliminary Version of the third Catalogue of Nearby Stars, 1991) includes over 1850 stars which lie north of δ 30° and are either identified as spectral type M, or are unclassified but with an absolute visual magnitude estimate MV>+8.O. Although there is no uniformity in selection criteria, and many of the stars lack basic data (radial velocities, spectral types, accurate photometry), the observational properties of these stars underlie most estimates of the fundamental characteristics of the Galactic Disk. We have obtained optical spectroscopy of 1746 of the 1876 stars-the remaining 130 are binary companions of brighter stars and inaccessible to our observations. These spectra allow us, first, to exclude 61 stars as either degenerates or as misclassified earlier-type (B - K) stars lying beyond the 25 pc limit; to establish radial velocities accurate to ±10 km s-1 for all stars confirmed as late-type dwarfs; to determine spectral types and absolute magnitudes from the TiO bandstrength, allowing more accurate distance estimates for stars with inaccurate (or no) trigonometric parallax measurements; and to identify stars with Ha emission (chromospherically active stars) and with strong CaH absorption (perhaps including some metal-poor disk subdwarfs). We have determined the nearby-star luminosity function from complete samples derived by applying both the distance limits defined by Wielen (1974) and by using limits derived from our own analysis. In both cases, we find good agreement with Wielen's results to MV ∼+11, but lower densities at the maximum (MV∼+12). The latter analysis results in a luminosity function, ΦCNS, which closely matches photometric parallax analyses for MV<+11 and MV>+14 -- we do not recover the apparent excess of low-luminosity stars inferred from analysis of the 5 pc sample. However, ΦCNS does lie below Φphot at the peak (MV∼12), and we suggest that this offset is caused by the inclusion of unrecognized binaries in the photometric surveys. We have also reanalyzed the local stellar kinematics using the complete sample and find that the velocity distributions show significant departures from single Gaussian velocity dispersions.