A comparison of different spectral classification systems for early type stars using HIPPARCOS parallaxes

Abstract

An ``inventory'' of different classification systems were made. Two different surveys for B9 to F2 type stars were chosen in oder to get an unbiased sample of ``normal'' stars. Jaschek & Valbousquet (1997) and Jaschek & Gómez (1998) already investigated the intrinsic consistency of the MK spectral classification systems. But interesting enough their results contradict in some important points. With the help of Hipparcos parallaxes, a comparison of the luminosity classes V, IV and III was performed using absolute magnitudes in order to find significant deviations from the ``classical'' picture (M_V(III) brighter than M_V(V) for the same spectral type). The main result is that luminosity class IV is completely covered by luminosity class V and III, furthermore only the brightest luminosity class III objects are distinct from luminosity class V stars. This conclusion is based on a large sample of stars from different classification surveys. Otherwise these surveys give comparable intrinsic errors. Based on data obtained from the ESA Hipparcos astrometry satellite