Inferring Coronal Structure from X‐Ray Light Curves and Doppler Shifts: AChandraStudy of AB Doradus

The Chandra X-ray observatory monitored the single cool star, AB Doradus,continuously for a period lasting 88 ksec (1.98 Prot) in 2002 December with theLETG/HRC-S. The X-ray lightcurve shows rotational modulation, with three peaksthat repeat in two consecutive rotation cycles. These peaks may indicate thepresence of compact emitting regions in the quiescent corona. Centroid shiftsas a function of phase in the strongest line profile, O VIII 18.97 A, indicateDoppler rotational velocities with a semi-amplitude of 30 +/- 10 km/s. Bytaking these diagnostics into account along with constraints on the rotationalbroadening of line profiles (provided by archival Chandra HETG Fe XVII and FUSEFe XVIII profile) we can construct a simple model of the X-ray corona thatrequires two components. One of these components is responsible for 80% of theX-ray emission, and arises from the pole and/or a homogeneously distributedcorona. The second component consists of two or three compact active regionsthat cause modulation in the lightcurve and contribute to the O VIII centroidshifts. These compact regions account for 16% of the emission and are locatednear the stellar surface with heights of less than 0.3R*. At least one of thecompact active regions is located in the partially obscured hemisphere of theinclined star, while one of the other active regions may be located at 40degrees. High quality X-ray data such as these can test the models of thecoronal magnetic field configuration as inferred from magnetic Zeeman Dopplerimaging.Comment: 28 pages, 11 figures, accepted by Ap