Astron. Astrophys. 324, 155-160 (1997)

Simultaneous optical and ROSAT X-ray observations of the classical
T Tauri star BP Tauri ^*

E. Gullbring ^{1, 4}, H. Barwig ² and J.H.M.M. Schmitt <sup>3

1</sup> Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden
² Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München, Germany
³ Max-Planck-Institut für Extraterrestrische Physik, D-85748 Garching, Germany
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden street, Cambridge, MA, 02138, USA

Received 3 January 1996 / Accepted 24 February 1997

Abstract

The classical T Tauri star BP Tauri has been simultaneously observed with UBVRI high-speed photometry at a time resolution of 2 sec and with the ROSAT PSPC detector during five nights. BP Tauri showed brightness variations on time scales ranging from nights to hours both in the optical and in the X-ray band, however, the night-to-night variations in the optical and X-ray spectral regions were not correlated. On one occasion, a short term optical event with an amplitude in U of and a time duration of 1.2 hours occurred, with no corresponding increase in the X-ray count rate during the decay of the event. In conclusion, the observations show that there are no detectable correlations between the optical and X-ray variability of BP Tau on time scales ranging from 1 hour to days. We discuss the possibility that the optical variability of BP Tau is related to accretion of circumstellar material onto the central star, while the X-ray emission presumably comes from magnetically active regions.

Key words: stars: activity flare pre-main-sequence stars: individual: BP Tauri X-rays: stars

* Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie, Heidelberg

Send offprint requests to: E. Gullbring egullbring@cfa.harvard.edu

SIMBAD Objects

Contents

• 1. Introduction
• 2. Summary of observations
• 3. Statistical significance of the data and observational results
  • 3.1. The optical data
  • 3.2. The X-ray data
  • 3.3. Relation between the optical and X-ray variability
• 4. Origin of the optical and X-ray variability
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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