Phase-Dependent Velocity Shift of the O VI Broad Wing Emission from AB Dor

Astronomy and Astrophysics – Astronomy

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Scientific paper

AB Dor is a 30 million year old K0 star dwarf that has recently arrived on the main sequence. It is a rapid rotator (P=12.5 h; v sin i = 80 km/s), and it is extremely active. Coronal flares, H-alpha absorption from prominences, a changing distribution of photospheric spots, and rotationally-modulated ultraviolet emission line fluxes have all been observed from this system. In order to establish the spatial character of the active regions, it is crucial that the system be observed continuously for at least two full rotations. AB Dor was observed with FUSE during October and December 1999 (but for less than 1 full rotational cycle each time) and again (for over two rotations) in December 2003. A preliminary analysis of the time-averaged O VI and C III line profiles observed with FUSE showed a significant variation in the line profiles obtained 4 years apart. The profiles obtained 2 months apart are similar, but not identical. In order to search for the short timescale variability, and to determine whether it is periodic (and therefore indicative of the spatial distribution of magnetic activity on the surface), we have reanalyzed all three archival FUSE data sets of AB Dor using the latest calibration software. We present results derived from multi-gaussian fits to the emission line profiles with a time resolution of about 1 hour, and from the total emission line flux light curve with a time resolution of a few minutes. In addition to flares and sporadic variability, there was a clearly phase-dependent velocity shift between the narrow core and the broad wings of the O VI emission line.

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