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Astron. Astrophys. 337, 403-412 (1998)


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Evolutionary models for solar metallicity low-mass stars: mass-magnitude relationships and color-magnitude diagrams *

I. Baraffe 1, G. Chabrier 1, F. Allard 1, 2 and P.H. Hauschildt 3

1 C.R.A.L. (UMR 5574 CNRS), Ecole Normale Supérieure, F-69364 Lyon Cedex 07, France (ibaraffe, chabrier, fallard @ens-lyon.fr)
2 Department of Physics, Wichita State University, Wichita, KS 67260-0032, USA (allard@eureka.physics.twsu.edu)
3 Department of Physics and Astronomy and Center for Simulational Physics, University of Georgia Athens, GA 30602-2451, USA (yeti@hobbes.physast.uga.edu)

Received 16 February 1998 / Accepted 11 May 1998

Abstract

We present evolutionary models for low mass stars from 0.075 to 1 [FORMULA] for solar-type metallicities [M/H]= 0 and -0.5. The calculations include the most recent interior physics and the latest generation of non-grey atmosphere models. We provide mass-age-color-magnitude relationships for both metallicities. The mass-MV and mass-MK relations are in excellent agreement with the empirical relations derived observationally. The theoretical color-magnitude diagrams are compared with the sequences of globular clusters (47 Tucanae) and open clusters (NGC2420 and NGC2477) observed with the Hubble Space Telescope. Comparison is also made with field star sequences in [FORMULA]-[FORMULA], [FORMULA]-[FORMULA] and [FORMULA]-[FORMULA] diagrams. These comparisons show that the most recent improvements performed in low-mass star atmosphere models yield now reliable stellar models in the near-infrared. These models can be used for metallicity, mass, temperature and luminosity calibrations. Uncertainties still remain, however, in the optical spectral region below [FORMULA], where predicted (V-I) colors are too blue by 0.5 mag for a given magnitude. The possible origins for such a discrepancy, most likely a missing source of opacity in the optical and the onset of grain formation are examined in detail.

Key words: stars: low-mass, brown dwarfs – stars: evolution – stars: Hertzsprung-Russel (HR) and C-M diagrams – stars: interiors – stars: atmospheres

* Tables 1 to 3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr/pub/cats/J/A+A/337/403 (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/337/403

© European Southern Observatory (ESO) 1998

Online publication: August 17, 1998

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