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Effect of the microturbulence parameter on the Color-Magnitude Diagram

Published online by Cambridge University Press:  01 August 2006

J. Montalbán ,
J. Nendwich ,
U. Heiter ,
F. Kupka ,
E. Paunzen  and
B. Smalley
J. Montalbán
Affiliation:
Institut d'Astrophysique et Géophysique, Université de Liège, 4000-Liége, Belgium email: j.montalban@ulg.ac.be
J. Nendwich
Affiliation:
Institut für Astronomie, Vienna, Austria, email: nendwich@astro.univie.ac.at, ernst.paunzen@astro.univie.ac.at
U. Heiter
Affiliation:
Department of Astronomy and Space Physics, Uppsala University, Uppsala, Sweden, email: ulrike@astro.uu.se
F. Kupka
Affiliation:
Max-Planck-Institute for Astrohysics, Garching, Germany, email: fk@mpa-garching.mpg.de
E. Paunzen
Affiliation:
Institut für Astronomie, Vienna, Austria, email: nendwich@astro.univie.ac.at, ernst.paunzen@astro.univie.ac.at
B. Smalley
Affiliation:
Keele University, Keele, UK email: bs@astro.keele.ac.uk
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Abstract

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Microturbulence is usually treated in model atmospheres as a free parameter (ξt) that allows to re-establish agreement among abundances derived from different lines. Even if this parameter is a consequence of treating a 3D problem as a 1D one, it seems clear that microturbulence is linked to the velocity field within the atmosphere, and therefore to convection in the external layers. The values of the parameter as determined from observations show a dependence both on effective temperature and on surface gravity. In this paper we study how the microturbulence parameter used in the atmosphere models affects the theoretical color-magnitude diagram (CMD). First, in the Main Sequence (MS) domain due to the dependence of the microturbulence parameter on Teff; and second, in the giant branch (Pre-main sequence and Red Giant Branch) where several photometric indexes show a large variation due to the increase of the microturbulence parameter as the stellar gravity decreases. We predict then a significant change in the CMD, as well as in the color-temperature calibrations, if variations of ξt such as those observationally determined are included in theoretical CMD computations.

Keywords

Convectionstars: fundamental parameters(stars:) Hertzsprung-Russell diagramstars: atmospheres
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S239: Convection in Astrophysics , August 2006 , pp. 166 - 168
Copyright
Copyright © International Astronomical Union 2007

References

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