Astron. Astrophys. 349, 485-494 (1999)

Consequences of Hipparcos parallaxes for stellar evolutionary models ^*

Three Hyades binaries: V 818 Tauri, 51 Tauri, and Tauri

E. Lastennet ^1,2, D. Valls-Gabaud ^2,3, Th. Lejeune ⁴ and E. Oblak <sup>5

1</sup> Astronomy Unit, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK
² UMR CNRS 7550, Observatoire Astronomique, 11, rue de l'Université, F-67000 Strasbourg, France
³ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
⁴ Astronomisches Institut der Universität Basel, Venusstrasse 7, CH-4102 Binningen, Switzerland
⁵ Observatoire de Besançon, 41 bis avenue de l'Observatoire, F-25010 Besançon, Cedex, France

Received 19 February 1999 / Accepted 19 May 1999

Abstract

Three binary systems in the Hyades open cluster (51 Tau, V818 Tau, and Tau), with known metallicity and good Johnson photometric data are used to test the validity of three independent sets of stellar evolutionary tracks. A statistical method is described and applied to the colour-magnitude diagram of the six selected components, giving rise to -contours in the metallicity-age plane. The effects of the Hipparcos parallaxes on these confidence regions are studied in detail for these binaries through a comparison with very accurate but older orbital parallaxes. There are no significant differences in 51 Tau and Tau, and hence the test validates the sets of theoretical tracks used. However the orbital parallax of V 818 Tau leads to metallicities too large in comparison with the observed range, while the Hipparcos parallax give consistent results, at the 1 level. Comparisons between the predicted and measured masses are also made and show a good agreement. However, even if the Padova tracks predict correct masses for each component of V 818 Tau, there is no Padova track that fits both components simultaneously in the mass-radius diagram. Finally, since the individual masses of these binaries are accurately known, some issues about the influence of the Hipparcos parallaxes on their location in the mass-luminosity diagram are also discussed.

Key words: stars: binaries: general stars: fundamental parameters stars: individual: 51 Tau; 2  Tau; V 818 Tau Galaxy: open clusters and associations: individual: Hyades

* Based on data from the ESA Hipparcos satellite

Send offprint requests to: E.Lastennet@qmw.ac.uk

SIMBAD Objects

Contents

• 1. Introduction
• 2. Statistical method description
• 3. Tests with well-detached binaries
  • 3.1. Results for 51 Tau
  • 3.2. Results for V 818 Tau
  • 3.3. Results for Tau
  • 3.4. The influence of the Hipparcos parallaxes on the Hyades mass-M_V relation
• 4. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999
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