Stellar Halo Parameters from 4588 Subdwarfs

Abstract

Using a reduced proper motion discriminator, I obtain a sample of 4588 subdwarfs from the Revised NLTT Catalog of Salim & Gould. The ample statistics and low contamination permit much more precise determinations of halo parameters than has previously been possible. The stellar halo is not moving with respect to the Local Standard of Rest (LSR) in either the vertical or radial direction, up to uncertainties of 2 km/s. This indicates that either the LSR is on a circular orbit or the Sun happens to lie very close to an extremum of the LSR's elliptical orbit. Similarly, tentative detections of vertical proper motion of Sgr A* relative to the LSR are either incorrect or they reflect real physical motion of the central black hole relative to the Galactic potential. The correlation coefficients of the halo velocity ellipsoid, which would reflect any possible misalignment between its principal axes and the cardinal directions of the Galaxy, vanish to within 2%. The halo subdwarf luminosity function peaks at M_V ~ 10.5 with a full width half maximum of about 2.5 mag.