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Synthetic photometry from ATLAS9 models in the UBV Johnson system
Received 22 December 1998 / Accepted 18 March 1999
Several grids of synthetic UBV color indices computed in the Johnson system and based on ATLAS9 atmospheric models are compared and discussed.
We present synthetic colors which differ from those computed by Kurucz (1995) only for the convective models and for a very small shift of the zero-points. We compare these colors, called C97, with colors computed by Kurucz (1993a), Kurucz (1995) (K95), Bessell et al. (1998) (BCP). The Buser & Kurucz (1992) (BK92) colors, derived from models different from ATLAS9, are also considered. -(U-B), -(B-V), and -BCV relations are compared together and are compared with empirical relations from literature.
For convective stars ( 8750 K), differences related with the different synthetic grids based on the ATLAS9 models are not larger than 100 K for [M/H] = 0.0 and 200 K for [M/H] = -2.0.
All the K95, C97, and BCP grids give, in general, larger than those from the empirical -color relations. For dwarfs, at = 5000 K and for [M/H] = 0.0, from (U-B) is about 250 K, and from (B-V) is on the order of 200 K. For giants, computed and observed -(U-B) data agree well, while, for (B-V), the behaviour is similar to that for dwarfs. These results do not change in a significant way for different metallicities.
Computations performed for [M/H] = -2.0 have shown that, for dwarfs, the agreement with the observations improves when models computed for solar scaled abundances, but with elements enhanced by 0.4 dex and based on the new solar iron abundance log(NFe/Ntot) = -4.53 dex, are used.
The dependence of the color indices on Teff, gravity, metallicity, and microturbulent velocity is investigated.
Key words: techniques: photometric stars: atmospheres stars: fundamental parameters
Send offprint requests to: F. Castelli
Correspondence to: firstname.lastname@example.org
Online publication: May 21, 1999