Astron. Astrophys. 363, 675-691 (2000)

Calibrations of Centauri A & B

P. Morel ¹, J. Provost ¹, Y. Lebreton ², F. Thévenin ¹ and G. Berthomieu <sup>1

1</sup> Département Cassini, UMR CNRS 6529, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice CEDEX 4, France
² DASGAL, UMR CNRS 8633, Observatoire de Paris-Meudon, 92195 Meudon Principal CEDEX, France

Received 6 July 2000 / Accepted 28 September 2000

Abstract

Detailed evolutionary models of the visual binary Centauri, including pre main-sequence evolution, have been performed using the masses recently determined by Pourbaix et al. (1999). Models have been constructed using the CEFF equation of state, OPAL opacities, NACRE thermonuclear reaction rates and microscopic diffusion. A -minimization is performed to derive the most reliable set of modeling parameters , where is the age of the system, the initial helium content, the initial metallicity and, and the convection parameters of the two components. Using the basic Böhm-Vitense (1958) mixing-length theory of convection, we derive . We obtain a noticeably smaller age than estimated previously, in agreement with Pourbaix et al. (1999), mainly because of the larger masses. If convective core overshoot is considered we get . The use of Canuto & Mazitelli (1991 , 1992) convection theory leads to the set . Using the observational constraints adopted by Guenther & Demarque (2000), and the basic mixing-length theory, we obtain and surface lithium depletions close to their observed values.

A seismological analysis of our calibrated models has been performed. The determination of large and small spacings between the frequencies of acoustic oscillations from seismic observations would help to discriminate between the models of Cen computed with different masses and to confirm or rule out the new determination of masses.

Key words: convection diffusion stars: binaries: visual stars: evolution stars: fundamental parameters stars: individual: ff Cen

Send offprint requests to: P. Morel

Correspondence to: Pierre.Morel@obs-nice.fr

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Contents

• 1. Introduction
• 2. Previous theoretical works
• 3. The puzzle of the mixing-length parameter
• 4. Diffusion and transport processes
• 5. Observations of the visual binary Cen
  • 5.1. Astrometric data
  • 5.2. Photometric data
  • 5.3. Spectroscopic data and atmospheric parameters
    • 5.3.1. Effective temperatures
    • 5.3.2. Surface gravities
    • 5.3.3. Chemical composition
    • 5.3.4. Rotation
  • 5.4. Seismological observations
  • 5.5. Adopted observables constraining the models
• 6. The method of calibration
• 7. Evolutionary models
  • 7.1. Nuclear and diffusion network
  • 7.2. Equation of state, opacities, convection and atmosphere
  • 7.3. Numerics
• 8. Results
  • 8.1. models
  • 8.2. models
  • 8.3. Seismological analysis of Cen A & B
    • 8.3.1. p-mode oscillations
    • 8.3.2. g-mode oscillations
• 9. Discussion and conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
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