THE LUMINOSITY AND MASS FUNCTIONS OF LOW-MASS STARS IN THE GALACTIC DISK. II. THE FIELD

Abstract

We report on new measurements of the luminosity function (LF) and mass function (MF) of field low-mass dwarfs derived from Sloan Digital Sky Survey Data Release 6 photometry. The analysis incorporates ~15 million low-mass stars (0.1 M[subscript ʘ] < M < 0.8 M[subscript ʘ]), spread over 8400 deg[superscript 2]. Stellar distances are estimated using new photometric parallax relations, constructed from ugriz photometry of nearby low-mass stars with trigonometric parallaxes. We use a technique that simultaneously measures Galactic structure and the stellar LF from 7 < M[subscript r] < 16. We compare the LF to previous studies and convert to an MF using the mass-luminosity relations of Delfosse et al. The system MF, measured over –1.0< log M/M[subscript ʘ] <–0.1, is well described by a lognormal distribution with M[subscript ο] = 0.25 M[subscript ʘ]. We stress that our results should not be extrapolated to other mass regimes. Our work generally agrees with prior low-mass stellar MFs and places strong constraints on future theoretical star formation studies.