Astron. Astrophys. 356, 541-558 (2000)

Multiplicity of X-ray selected T Tauri stars in the Scorpius-Centaurus OB association ^*

R. Köhler ^1,2, M. Kunkel ², C. Leinert ² and H. Zinnecker <sup>1

1</sup> Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Received 3 September 1999 / Accepted 24 November 1999

Abstract

We report the results of a search for binarity among young stars, performed in the Scorpius-Centaurus OB association on a sample of 118 X-ray selected T Tauri stars. We use speckle interferometry and direct-imaging observations to find companions in the separation range - . After corrections to account for confusion with background stars and for the bias induced by the X-ray selection, we find a multiplicity (number of binaries or multiples divided by number of systems) of , and a number of companions per system of . This is higher by a factor of compared to main-sequence stars, but slightly lower than in a sample in the Taurus-Auriga star-forming region that was selected and studied similary. In Scorpius-Centaurus, we find fewer binaries with nearly equal brightness than in Taurus-Auriga. There are significant differences between the period distributions in the two subgroups Upper Scorpius A and B: The peak of the distribution of stars in US-A is at about days, while that of stars in US-B is around days. We compared our results with the optical multiplicity survey of Brandner et al. (1996), whose sample contains 49 stars that were also observed by us, and find no infrared companions. The flux ratio distributions of close and wide binaries in our sample show no significant difference.

Key words: stars: pre-main sequence stars: binaries: visual infrared: stars surveys techniques: interferometric

* Based on observations obtained at the European Southern Observatory, La Silla

Send offprint requests to: Rainer Köhler, AIP

Correspondence to: rkoehler@aip.de

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Contents

• 1. Introduction
• 2. The sample
• 3. Observations and data analysis
• 4. Results
  • 4.1. Uncorrected data
  • 4.2. The restricted sample
  • 4.3. Confusion with background stars
  • 4.4. Bias induced through X-ray selection
    • 4.4.1. Stars discovered by Walter et al.
    • 4.4.2. Stars discovered by Kunkel
    • 4.4.3. Unresolved stars affected by the X-ray bias
• 5. Discussion
  • 5.1. Stars discovered with EINSTEIN compared to stars discovered with ROSAT
  • 5.2. Pre-main-sequence compared to main-sequence stars
  • 5.3. Scorpius-Centaurus compared to Taurus-Auriga
  • 5.4. Comparison of subgroups in Ophiuchus-Scorpius-Centaurus
  • 5.5. Infrared companions
  • 5.6. Are the flux ratios of close and wide companions different?
  • 5.7. Dependence of multiplicity on spectral type
• 6. Summary and conclusions
• Acknowledgements
• Appendices
  • A: A brief introduction to speckle interferometry
• References

© European Southern Observatory (ESO) 2000

Online publication: April 10, 2000
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