Professor James Binney FRS

Abstract:

The basic data discussed here consist of parallaxes and apparent magnitudes of more than 6000 stars with delta < -26 degrees from the Hipparcos Catalogue which were selected from the Michigan Spectral Catalogue to have estimated spectroscopic distances within 80 parsecs. The statistical properties of the sample are briefly discussed, and the luminosity function of main sequence stars is determined by the maximum-volume method from nearly 3000 stars with observed parallaxes greater than 12.5 mas.

Abstract:

We received a sample of 6840 Hipparcos stars south of declination -26 degrees that (i) have MK spectral types in the Michigan catalogues and (ii) had spectroscopic parallaxes that placed them within 80 pc of the Sun. Of these, 3727 are well determined as luminosity class V and actually lie within 100 pc. From this subsample we can determine the distribution in M-V of main-sequence stars of given spectral type for spectral types that range from early F to early K. These distributions are significantly non-Gaussian, but when fitted to Gaussians they yield central values of M-V in good agreement with earlier estimates of the absolute magnitudes of main-sequence stars. We also determine anew the distribution of B-V at each spectral type. We find that the dispersion in B-V at given spectral type is very small.