Professor James Binney FRS

Abstract:

We analyze a kinematically unbiased sample of 5610 stars around the south celestial pole that (i) have MK spectral types in the Michigan catalogues with luminosity class V and (ii) had photometric parallaxes that placed them within 80 pc of the Sun. We bin the stars by B - V and determine for each bin the solar motion from proper motions alone. As expected, the U and W components of the derived solar motions do not vary significantly from bin to bin, while the V component varies systematically. As the classic Stromberg relation predicts, V is a linear function of the variance S-2 within each bin around the solar motion. Extrapolating V (S-2) to S = 0 we determine the solar motion with respect to the LSR, obtaining a significantly smaller value of V than is usually employed. Parenago's discontinuity in the dependence of S-2 on spectral type emerges with exceptional clarity.

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.