The Luminosity and Mass Functions of Low-Mass Stars in the Galactic Disk. Ii. The Field

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 (SDSS) Data Release 6 (DR6) photometry. The analysis incorporates ~15 million low-mass stars (0. 1 Msun < M < 0. 8 Msun), spread over 8, 400 square degrees. 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 < Mᵣ < 16. We compare the LF to previous studies and convert to a MF using the mass-luminosity relations of Delfosse et al. , 2000. The system MF, measured over -1. 0 < log M/Msun < -0. 1, is well-described by a log-normal distribution with Mo = 0. 25 Msun. 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 star-formation studies of the Milky Way.