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

II. Temperature determination and three “standard” stars

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 [CITE] 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.