SIMULTANEOUS ORPEUS FUV AND ROSAT X-RAY OBSERVATIONS OF THE YOUNG RAPID ROTATOR AB DORADUS

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 lin es of CIII at 977 Angstrom and OVI at 1032 and 1038 Angstrom are clear ly detected in the ORFEUS spectrum. The overall emission measure distr ibution of the combined FUV and X-ray data is steeply rising. The OVI 1032 Angstrom line is definitely broadened with respect to the instrum ental line profile, however, the observed broadening does not exceed t he photospheric upsilon sin(i)-value. This strongly suggests that the observed OVI emission, formed at a characteristic temperature of appro ximate to 300000 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.