Astron. Astrophys. Suppl. Ser. 142, 13-24
N. Ginestet1 - J.M. Carquillat1 et C. Jaschek2
1 - Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique (UMR 5572), 14 avenue Edouard Belin, 31400 Toulouse, France
2 - Observatoire de Strasbourg, URA 1280 (CNRS), 11 rue de l'Université, 67000 Strasbourg, France
Reçu le 20 juillet ; accepté le 10 novembre, 1999
Contrary to what is claimed in other papers, the absolute magnitude domain devoted to the giant stars does not overlap the domain of dwarfs. We find that the discrepancies between absolute magnitudes from Hipparcos data and absolute magnitudes deduced from Schmidt-Kaler calibrations increase with the relative error on the parallaxes. So, for only 3% of the stars present a discrepancy of one luminosity class, while this percentage reaches 54% for .
Curiously, the luminosity of the giants seems to increase with the distance of the stars, whereas the supergiants of the sample appear underluminous at least for d < 600 pc!
We point out a list of 14 MK standards whose luminosity classes may be erroneous and need a new spectral classification, in the near infrared. The case of composite-spectrum binaries is also discussed. Most of these are too distant for accurate parallaxes even with Hipparcos: only sixteen stars have ; for these, we give new spectral classifications in agreement with both our classifications in the near infrared of the cool components and Hipparcos data.
Finally, for stars having high-precision parallaxes ( ) there is no serious problem for Schmidt-Kaler calibrations whith respect to Hipparcos data. The data corresponding to parallaxes of lower precisions should be used with caution and only for statistical analyses.
Key words: stars: fundamental parameters -- stars: distances
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