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Astron. Astrophys. 363, 667-670 (2000)

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Research Note

An X-ray flare from the Lindroos binary system HD 560

B. Stelzer and N. Huélamo

Max-Planck-Institut für extraterrestrische Physik, 85740 Garching, Germany

Received 23 August 2000 / Accepted 11 October 2000


We report on a large X-ray flare from the Lindroos binary system HD 560 during a pointed ROSAT PSPC observation. HD 560 is composed of a B9 and a G5 type star. The late-type companions in bound Lindroos binaries are Post T Tauri star (PTTS) candidates, i.e. pre-main sequence stars on their final approach to the main sequence. Strong (magnetic) activity is, therefore, expected for the G star, in contrast to the late-B type component for which no mechanism of X-ray production is known. The system is unresolved in the ROSAT image.

During outburst the count rate has changed by at least a factor of 2, and presumably more (the maximum was not observed). The peak luminosity measured is [FORMULA], comparable to the largest values derived for flares on pre-main sequence T Tauri stars. A two-temperature model for thermal emission from a hot, optically thin plasma shows an increase of the higher temperature as a result of coronal heating during the flare. The lower temperatures do not change during outburst.

Key words: X-rays: stars – stars: binaries: general – stars: individual: HD 560 – stars: late-type – stars: activity

Send offprint requests to: B. Stelzer

Correspondence to: stelzer@xray.mpe.mpg.de

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000