The absolute magnitude of the early type MK standards from HIPPARCOS parallaxes

Abstract

We analyse the standards of the MK system with the help of Hipparcos parallaxes, using only stars for which the error of the absolute magnitude is <= 0.3 mag. We find that the main sequence is a wide band and that, although in general giants and dwarfs have different absolute magnitudes, the separation between luminosity classes V and III is not clear. Furthermore, there are a number of exceptions to the strict relation between luminosity class and absolute magnitude. We analyse similarly the system of standards defined by Garrison & Gray (1994) separating low and high rotational velocity standards. We find similar effects as in the original MK system. We propose a revision of the MK standards, to eliminate the most deviant cases. Based on data from the ESA Hipparcos astrometry satellite