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Astron. Astrophys. 325, 249-254

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Simultaneous ORFEUS FUV and ROSAT X-ray observations
of the young rapid rotator AB Doradus

Jürgen H.M.M. Schmitt1, J. Krautter2, I. Appenzeller2, H. Mandel2, R. Wichmann2, J. Barnstedt3, M. Gölz3, M. Grewing3, W. Gringel3, C. Haas3, W. Hopfensitz3, N. Kappelmann3, and G. Krämer3

1Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany
2Landessternwarte Königstuhl, D-69117 Heidelberg, Germany
3Institut für Astronomie und Astrophysik Tübingen, Germany

Received 18 December 1996 / Accepted 11 March 1997


We present simultaneous soft X-ray and FUV observations of the rapidly rotating young star AB Doradus (HD 36705), obtained with the position sensitive proportional counter (PSPC) on board ROSAT and the FUV/EUV spectrometer on board ORFEUS. The X-ray data show that AB Dor was in a high state, possibly in a flare, during the FUV observations. The lines of CIII at 977 Å and OVI at 1032 and 1038 Å are clearly detected in the ORFEUS spectrum. The overall emission measure distribution of the combined FUV and X-ray data is steeply rising. The OVI 1032 Å line is definitely broadened with respect to the instrumental line profile, however, the observed broadening does not exceed the photospheric v sin(i)-value. This strongly suggests that the observed OVI emission, formed at a characteristic temperature of FORMULA K, is produced almost exclusively relatively close to the star's surface, and not in an extended corotating emission region with scale sizes of a few stellar radii.

Key words: stars: coronae - stars: activity - stars: late-type - stars: rotation - stars: individual: AB Dor

Send offprint requests to: J.H.M.M. Schmitt (jhs@rosat.mpe-garching.mpg.de)

© European Southern Observatory (ESO) 1997