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

Free access article

Issue		A&A Volume 426, Number 1, October IV 2004


Page(s)		309 - 322
Section		Stellar atmospheres
DOI		http://dx.doi.org/10.1051/0004-6361:20040456

A&A 426, 309-322 (2004)
DOI: 10.1051/0004-6361:20040456

II. Temperature determination and three "standard" stars

F. Grupp

Universitäts Sternwarte München, Scheinerstr. 1, 81679 München, Germany
e-mail: fug@usm.uni-muenchen.de

(Received 16 March 2004 / Accepted 17 June 2004)

Abstract
The influence of the new MAFAGS-OS opacity sampling model atmosphere and its changed thermal structure is tested on two of the major methods to determine stellar effective temperatures: the infrared flux method and the Balmer line method. Both methods are shown to be affected by the new model. How a change of the resonance broadening theory according to Ali & Griem (1965) improves the theoretical Balmer line spectrum of the Sun is studied.

The new model together with the modified resonance broadening cross sections for hydrogen are then applied to three stars: Procyon, Groombridge 1830 and HD 19445. Stellar parameters measured for these stars lead to new determinations of masses, ages and spectroscopic distances for these objects. While Procyon's parameters are only slightly changed with respect to recent ODF-based analyses, the temperatures of Groombridge 1830 and HD 19445 are significantly increased, leading to higher masses and lower ages for these two stars. Compared to ODF-based studies, the paradox of Groombridge 1830 and HD 19445 having ages well above the age of the Universe is resolved and the determined spectroscopic parallaxes are in very good agreement with high precision HIPPARCOS astrometry.

Key words: methods: numerical -- stars: individual: Procyon -- stars: individual: Groombridge 1830 -- stars: individual: HD 19445 -- stars: atmospheres -- Sun: fundamental parameters

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