Astron. Astrophys. 326, 709-721 (1997)

Absolute dimensions of eclipsing binaries

XXI. V906 Scorpii: a triple system member of M 7 ^*

S.H.P. Alencar ¹, L.P.R. Vaz ¹ and B.E. Helt <sup>2

1</sup> Departamento de Fsica, ICEx, UFMG, Caixa Postal 702, 30.161-970 Belo Horizonte, MG, Brazil
² Niels Bohr Institute for Astronomy, Physics and Geophysics; Astronomical Observatory, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark

Received 24 December 1996 / Accepted 29 April 1997

Abstract

We present an analysis based on new uvby  light curves and spectroscopic data of the detached triple-lined B-type eclipsing binary V906 Sco. The uvby light curves are analysed with an extended version of the Wilson-Devinney program. The spectroscopic CCD observations are analysed with both the Sterne and the Lehmann-Filhés methods. We conclude from the combined analysis that the triple system V906 Sco is a member of the open cluster M 7 and that its B-type eclipsing components are still on the main sequence, at an age of  yrs, already close to the TAMS (especially the more massive one). The system is older than the time for circularization of the orbit, and the small eccentricity is probably caused by the third component, which, however, is unlikely to be the main responsible for the apsidal motion, probably more influenced by tidal and rotational deformation. We determine absolute dimensions of high precision (errors ): , , and , in solar units. The system is detached, with both components in synchronous rotation, and therefore representative for normal stars.

Key words: binaries: eclipsing -- stars: fundamental parameters -- stars: evolutionstars: individual: V906 Sco

* Based on observations collected with the 1.6 m telescope of the Pico dos Dias Observatory, National Laboratory of Astrophysics, LNA-CNPq, Brasópolis, MG, Brazil and with the Danish 50 cm telescope (SAT) at the European Southern Observatory (ESO), La Silla, Chile

Send offprint requests to: L.P.R. Vaz

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Contents

• 1. Introduction
• 2. Spectroscopic analysis
  • 2.1. Radial-velocity curves and the mass ratio
  • 2.2. Rotation rates and luminosity ratios
• 3. Photometric analysis
  • 3.1. Observations
  • 3.2. Ephemeris and period analysis
  • 3.3. Photometric elements
    • 3.3.1. Starting values and initial solutions
    • 3.3.2. Final solutions with the WD model
• 4. Discussion
  • 4.1. Interstellar absorption and bolometric corrections
  • 4.2. Absolute dimensions
  • 4.3. Evolutionary models
  • 4.4. Orbit circularization
  • 4.5. Apsidal motion
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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