Issue |
Astron. Astrophys. Suppl. Ser.
Volume 142, Number 1, February II 2000
|
|
---|---|---|
Page(s) | 13 - 24 | |
DOI | https://doi.org/10.1051/aas:2000135 | |
Published online | 15 February 2000 |
Magnitudes absolues des étoiles standards MK des types G à M à partir des parallaxes Hipparcos
The absolute magnitudes of the G to M type MK standards from the Hipparcos parallaxes
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
Received:
20
July
1999
Accepted:
10
November
1999
We analyse a sample of about 500
MK standards of cool spectral types (G to M)
for to compare the visual absolute
magnitudes obtained from both Hipparcos
data and Schmidt-Kaler calibrations. Our
purpose is to validate our spectroscopic work
(Ginestet et al. 1997, 1999) on stars with
composite spectra with the help of Hipparcos
data.
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
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
© European Southern Observatory (ESO), 2000