Astron. Astrophys. 352, 479-488 (1999)

Investigation of the Praesepe cluster ^*

III. Radial velocity and binarity of the F5-K0 Klein-Wassink stars

J.-C. Mermilliod ¹ and M. Mayor <sup>2

1</sup> Institut d'Astronomie de l'Université de Lausanne, 1290 Chavannes-des-Bois, Switzerland
² Observatoire de Genève, 1290 Sauverny, Switzerland

Received 20 July 1999 / Accepted 2 November 1999

Abstract

Coravel observations of 103 F5-K0 stars in the Praesepe cluster yielded 24 spectroscopic binaries (3 are non-members), and 20 orbits were determined, with periods from 4 to 7400 days. Based on a complete sample in the colour range (80 stars, including KW 244 = TX Cnc), the companion star fraction CSF = 0.45. The percentage of spectroscopic binaries with P is 20% (16/80). The combined photometric and spectroscopic analysis showed that 12 among 18 single-lined spectroscopic binaries are located within the "single" star sequence in the diagram and cannot be detected by the photometric analysis in the UBV system. In addition, seven photometrically analysed binaries were not detected with the radial velocity observations, but are confirmed members. The number of single:binary:triple stars is 47:30:3.

Key words: Galaxy: open clusters and associations: individual: Praesepe stars: binaries: spectroscopic

* based on observations collected at the Haute-Provence Observatory (France)

Correspondence to: Jean-Claude.Mermilliod@obs.unige.ch

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations
  • 2.1. The sample
  • 2.2. Coravel observations
• 3. Results
  • 3.1. Membership
  • 3.2. Spectroscopic binaries
  • 3.3. Individual stars
  • 3.4. Binary frequency
  • 3.5. Mass ratios
  • 3.6. Cluster mean velocity
• 4. Colour-magnitude diagram
• 5. X-ray sources
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: December 2, 1999
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