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

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Consequences of Hipparcos parallaxes for stellar evolutionary models *

Three Hyades binaries: V 818 Tauri, 51 Tauri, and [FORMULA] Tauri

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

1 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


Three binary systems in the Hyades open cluster (51 Tau, V818 Tau, and [FORMULA] 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 [FORMULA]-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 [FORMULA] 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[FORMULA] 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

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999