A&A Supplement Ser., Vol. 124, July 1997, 359-384
Received July 18; accepted November 27, 1996
S.V. Mallik
Send offprint request: S.V. Mallik
Indian Institute of Astrophysics,
Bangalore 560034, India
CCD spectra of the infrared triplet lines of ionized calcium at
8498, 8542, 8662 have been obtained at a spectral resolution
of 0.4 Å in 146 stars brighter than V = +7.0 spanning a range in
spectral types from F7 to M4 of all luminosity classes and a range in
metallicity [Fe/H] from -3.0 to +1.1. These have been analysed to
investigate the dependence of the Ca II triplet strengths on stellar
parameters like luminosity, temperature and metallicity. A detailed study
reveals a strong dependence on luminosity, much stronger for metal rich
stars than for the metal poor ones and a milder dependence on metallicity,
although much more conspicuous in supergiants than in dwarfs. All these
correlations are found to be non-linear over the parameter space covered.
The present study also shows chromospheric activity to be an important
phenomenon affecting the strength and the shape of the line profiles. Stars
of similar luminosity and metallicity have varying Ca II line depths owing
to varying chromospheric emission filling in their Ca II absorption. The Ca
II triplet strength is thus observed to be a triparametric discriminant in
cool stars.
keywords: stars: late-type -- stars: chromospheres -- galaxies: stellar content