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

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 (MV(III) brighter than MV(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.