2004A&A...418..577D

We present the first far-UV spectra of the Herbig Be star HD 100546, observed by the Far Ultraviolet Spectroscopic Explorer (FUSE) as part of the Circumstellar Disks team program. We identified and analyzed numerous narrow absorption lines of circumstellar origin. Intense, broad and fairly asymmetric emission lines of CII, CIII, OVI and SII were also detected, spanning temperatures up to 3x10⁵K. Comparison of the spectra recorded two years apart reveals strong spectral variations, not only in the emission lines but also in the circumstellar lines of NI, NII, OI, ArI and FeII. The varying absorption lines of NI and OI exhibit the largest velocity width, from -200 to +320km/s, relative to the star's rest-frame. Variations on a timescale of an hour occurred only in the NI resonance triplet and OI (¹D) lines. The spectroscopic variability highlighted by these two observations and the line profile analysis reveal signatures of both outflow and infall processes, which appear to be related in this system. We suggest that these spectral signatures originate in a stellar magnetosphere, which likely interacts with the innermost part of the star's circumstellar disk. This interpretation can account for the main features observed in the spectrum of HD 100546: variable emission and absorption lines as well as suspected continuum variation.