Key points are not available for this paper at this time.
We have used new astrometric and spectroscopic observations to refine the volume-complete sample of M dwarfs defined in previous papers in this series. With the addition of Hipparcos astrometry, our revised VC2 sample includes 558 main-sequence stars in 448 systems. Analysis of that data set shows no evidence of any systematic kinematic bias. Combining those data with a Hipparcos-based sample of AFGK dwarfs within 25 pc of the Sun, we have derived the solar neighborhood luminosity function, Φ(MV), for stars with absolute magnitudes between -1 and +17. Using empirical and semiempirical mass-MV relations, we transform Φ(MV) to the present-day mass function, ψ(M) (=dN/dM). Depending on the mass-luminosity calibration adopted, ψ(M) can be represented by either a two-component or a three-component power law. In either case, the power-law index α has a value of ∼1.3 at low masses (0.1 M⊙ 4) stars in the Hipparcos 25 pc sample are well represented by two-component Gaussian distributions, with ∼10% of the stars in the higher velocity dispersion component. We suggest that the latter component is the thick disk, and we offer a possible explanation for the relatively low velocity dispersions shown by ultracool dwarfs.
Reid et al. (Thu,) studied this question.