Astron. Astrophys. 328, 349-360 (1997)

The role of convection on the uvby colours of A, F, and G stars ^*

B. Smalley ¹ and F. Kupka <sup>2

1</sup> Department of Physics, Keele University, Keele, Staffordshire, ST5 5BG, UK (bs@astro.keele.ac.uk)
² Inst. for Astronomy, Univ. of Vienna, Türkenschanzstr. 17, A-1180 Vienna, Austria (kupka@galileo.ast.univie.ac.at)

Received 28 April 1997 / Accepted 24 July 1997

Abstract

We discuss the effects of convection on the theoretical uvby colours of A, F, and G stars. The standard mixing-length theory ATLAS9 models of Kurucz (1993), with and without approximate overshooting, are compared to models using the turbulent convection theory proposed by Canuto & Mazzitelli (1991, 1992) and implemented by Kupka (1996a).

Comparison with fundamental and stars reveals that the Canuto & Mazzitelli models give results that are generally superior to standard mixing-length theory (MLT) without convective overshooting. MLT models with overshooting are found to be clearly discrepant. This is supported by comparisons of non-fundamental stars, with obtained from the Infrared Flux Method and from stellar evolutionary models for open cluster stars. The Canuto & Mazzitelli theory gives values of and that are in best overall agreement with observations.

Investigations of the index reveal that all of the treatments of convection presented here give values that are significantly discrepant for models with 6000 K. It is unclear as to whether this is due to problems with the treatment of convection, missing opacity, or some other reason. None of the models give totally satisfactory indices for hotter stars, but the Canuto & Mazzitelli models are in closest overall agreement above 7000 K.

Grids of uvby colours, based on the CM treatment of convection, are presented. These grids represent an improvement over the colours obtained from models using the mixing-length theory. The agreement with fundamental stars enables the colours to be used directly without the need for semi-empirical adjustments that were necessary with the earlier colour grids.

Key words: convection stars: atmospheres stars: general stars: fundamental parameters

* Table 5 is only available at the CDS via anonymous ftp 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html

Send offprint requests to: Barry Smalley

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Contents

• 1. Introduction
• 2. The treatment of convection
  • 2.1. Synthetic colours from convective model atmospheres
  • 2.2. New grids based on the CM model
• 3. Comparison with fundamental stars
  • 3.1. Effective temperature
  • 3.2. Surface gravity
• 4. Comparison with non-fundamental stars
  • 4.1. Effective temperature
  • 4.2. Surface gravity
• 5. Solar colours
• 6. Metallicity effects
• 7. Conclusion and future work
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: March 24, 1998

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