EDP Sciences
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Volume 420, Number 1, June II 2004
Page(s) 289 - 305
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20040971

A&A 420, 289-305 (2004)
DOI: 10.1051/0004-6361:20040971

MAFAGS-OS: New opacity sampling model atmospheres for A, F and G stars

I. The model and the solar flux
F. Grupp

Universitäts Sternwarte München, Scheinerstr. 1, 81679 München, Germany
(Received 5 January 2004 / Accepted 19 February 2004 )

We present a new opacity sampling model atmosphere code, named MAFAGS-OS. This code, designed for stars reaching from A0 down to G9 on a solar and metal poor main sequence and up to an evolutionary stage represented by the turnoff is introduced in its basic input physics and modelling techniques. Fe I bound-free cross-sections of Bautista (1997) are used and convection is treated according to Canuto & Mazzitelli (1991). An $\alpha_{\rm cm}$-parameter for the efficiency of convection of 0.82 is used as determined by Bemkopf (1998) from stellar evolution requirements.

Within the process of opacity sampling, special attention is drawn to the matter of line selection. We show that a selection criterion, in which lines are chosen by their opacity weighted relative to the continuous background opacity, is useful and valid.

The solar model calculated using this new code is shown to fit the measured solar flux distribution. It is also tested against the measured solar colours and leads to U-B=0.21 and B-V=0.64, in good agreement with observation. Comparison with measured centre-to-limb continuum data show only small improvement with respect to opacity-sampling type model atmospheres. This is the first of a series of 2 papers. Paper II will deal with the matter of temperature determination using Balmer lines and the infrared-flux method; furthermore it will present three "standard" stars analysed using this new model.

Key words: methods: numerical -- Sun: infrared -- Sun: photosphere -- stars: atmospheres -- stars: fundamental parameters

© ESO 2004