Astron. Astrophys. 331, 977-988 (1998)

Multiplicity of T Tauri stars in Taurus after ROSAT

Rainer Köhler and Christoph Leinert

Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany

Received 29 August 1997 / Accepted 12 November 1997

Abstract

We surveyed a sample of 75 T Tauri stars in the Taurus star forming region for companions. These stars were discovered with the help of ROSAT. The separation range covered is to , where the lower limit is given by the diffraction limit of the telescope and the upper limit by confusion with background stars. Combined with the results of the preceding survey by Leinert et al. (1993), we now have surveyed a sample of 178 young stars in Taurus, 63 classical, 106 weak-line, and 9 unclassified T Tauri stars. Within this sample, we find 68 binaries, 9 triples, and 3 quadruples. After corrections to account for confusion with background stars and for a bias induced through X-ray selection, we count 74 binaries or multiples with a total of 85 companions in 174 systems. This corresponds to a degree of multiplicity (number of binaries or multiples divided by number of systems) of , or to a duplicity, measured by the number of companions per system, of , which is higher by a factor of compared to solar-type main-sequence stars. We find no difference in duplicity between classical and weak-line T Tauri stars. There is a difference between close and wide pairs in the sense that close pairs have a flat distribution of flux ratios, while the flux ratios of wide pairs are peaked towards small values.

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

Send offprint requests to: Rainer Köhler (koehler@mpia-hd.mpg.de)

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Contents

• 1. Introduction
• 2. The sample
• 3. Observations
• 4. Results for the X-ray selected sample
  • 4.1. Uncorrected data
  • 4.2. Confusion with background stars
  • 4.3. Bias induced through X-ray selection
• 5. Discussion
  • 5.1. Comparison of the young star samples before and after ROSAT
  • 5.2. Pre-main-sequence vs. main-sequence stars
  • 5.3. Classical vs. weak-line T Tauri stars
  • 5.4. Surface density of companions
  • 5.5. Is there a difference between close and wide companions?
  • 5.6. Consequences of the controversy on the age of ROSAT-selected stars
• 6. Summary and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998
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