On the circumstellar environment of SS433

We present new 8200-8900 Å high-resolution spectroscopic observations of the unusual accreting source SS433. The spectra are highly variable on a night-to-night basis, and are dominated by emission from the Paschen series and O iemission. Differences in line profiles between the two species suggest that they arise in kinematically distinct and highly variable circumstellar regions. Moreover, the strength of O iemission argues against identifying the mass donor as a Wolf-Rayet star since we might expect oxygen to be depleted by the CNO cycle in such a star. Weak N iabsorption lines are present, which, if arising in the photosphere of the mass donor would imply a spectral type of B5 or later. However, no evidence was found for orbital modulation in their radial velocity curves suggesting that they too arise in the accretion-driven outflow. Finally, by analogy to the massive close binary RY Scuti, we suggest that the recent detection of a mid-infrared excess attributed to warm dust may arise in a circumbinary disc, implying that SS433 hosts a rich, highly structured circumstellar environment driven by the high mass-transfer rate from the mass donor