1996A&A...310..211S

We present spectropolarimetric observations of the symbiotic Mira V1016 Cygni which cover the broad emission features at λ6825 and λ7082. The λ6825 line, which is due to Raman scattering of O VI λ1032 emission, strongly increased its degree of polarization over a period of 3 years. The polarization angle in the blue line wing is found to rotate clock-wise at a constant rate of 8±2deg/yr. We interpret these changes as due to the binary motion. The binary axis, projected onto the celestial sphere was at a position angle of 81deg in August 1991 and rotated to 58deg in September 1994. The polarization changes in the λ6825 Raman line also indicate, that the V1016 Cyg system was close to conjunction in August 1991 and that the orbit inclination is 60±20deg. The binary period is most likely in the range of 80±25yrs. We find that the line of nodes of the orbital plane of V1016 Cyg has roughly a North-South orientation. This is in agreement with the bipolar outflow model proposed by Solf (1983) from emission line observations. The observed polarization structure in the Raman scattered O VI lines is not compatible with a scattering geometry which is rotationally symmetric around the binary axis. We adopt a 3-dimensional scattering model for the innermost region of the binary system. It consists of a Mira variable with a radially symmetric neutral wind region which is terminated on the hot components side by an ionization front which is warped due to the relative binary and wind motions. We identify in the spectrum of V1016 Cyg further Raman features: The broad emission bumps at λλ7023,7054 are due to Raman scattering of CIIλ1036,1037 at neutral hydrogen.