Astron. Astrophys. 359, 227-241 (2000)

X-ray emission from Lindroos binary systems

N. Huélamo ¹, R. Neuhäuser ¹, B. Stelzer ¹, R. Supper ¹ and H. Zinnecker <sup>2

1</sup> Max-Planck-Institut für Extraterrestrische Physik, 85740 Garching, Germany
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Received 10 December 1999 / Accepted 9 May 2000

Abstract

We present a study of the X-ray emission from binary systems extracted from the Lindroos catalogue (Lindroos 1986) based on the ROSAT All-Sky survey as well as ROSAT PSPC and HRI pointings. The studied sample consists of visual binary systems comprised of early-type primaries and late-type secondaries. The ages of the systems were determined by Lindroos (1985) from uvby photometry of the primaries. These ages range between 33 and 135 Myr, so if the late-type secondaries are physically bound to the early-type primaries, they could be Post-T Tauri stars (PTTS).

We have found strong X-ray emission from several secondaries. This fact together with their optical and IR data, make them bona fide PTTS candidates. We have also detected X-ray emission from several early-type primaries and, in particular, from most of the late-B type stars. Because their HRI hardness ratios are similar to those from resolved late-type stars, the presence of an unresolved late-type companion seems to be the cause of this emission.

Key words: stars: binaries: visual stars: early-type stars: pre-main sequence stars: individual: HR 4796 X-rays: stars

Send offprint requests to: N. Huélamo (huelamo@xray.mpe.mpg.de)

SIMBAD Objects

Contents

• 1. Introduction
• 2. The binary sample
• 3. ROSAT observations and data reduction
  • 3.1. PSPC observations
  • 3.2. HRI observations
  • 3.3. X-ray fluxes and luminosities
• 4. Interpretation of the data
  • 4.1. X-ray luminosity functions
  • 4.2. Hardness ratios
  • 4.3. X-ray luminosities
• 5. X-ray emission from late-type secondaries: are they Post T Tauri stars?
• 6. Results and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 30, 2000
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