Raman‐scattered Heiiλ6545 Line in the Symbiotic Star V1016 Cygni

We present a spectrum of the symbiotic star V1016 Cyg observed with the 3.6 mCanada-France-Hawaii Telescope, in order to illustrate a method to measure thecovering factor of the neutral scattering region around the giant componentwith respect to the hot emission region around the white dwarf component. Inthe spectrum, we find broad wings around H$\alpha$ and a broad emission featurearound 6545${\rm \AA}$ that is blended with the [N II]$ \lambda$ 6548 line.These two features are proposed to be formed by Raman scattering by atomichydrogen, where the incident radiation is proposed to be UV continuum radiationaround Ly$\beta$ in the former case and He II $\lambda$ 1025 emission linearising from $n=6\to n=2$ transitions for the latter feature. We remove theH$\alpha$ wings by a template Raman scattering wing profile and subtract the [NII] $\lambda$ 6548 line using the 3 times stronger [N II] $\lambda$ 6583feature in order to isolate the He II Raman scattered 6545 \AA line. We obtainthe flux ratio $F_{6545}/F_{6560}=0.24$ of the He II $\lambda$ 6560 emissionline and the 6545 \AA feature for V1016 Cyg. Under the assumption that the HeII emission from this object is isotropic, this ratio is converted to the ratio$\Phi_{6545}/\Phi_{1025}=0.17$ of the number of the incident photons and thatof the scattered photons. This implies that the scattering region with H Icolumn density $N_{HI}\ge 10^{20}{\rm cm^{-2}}$ covers 17 per cent of theemission region. By combining the presumed binary period $\sim 100$ yrs of thissystem we infer that a significant fraction of the slow stellar wind from theMira component is ionized and that the scattering region around the Miraextends a few tens of AU, which is closely associated with the mass lossprocess of the Mira component.Comment: 12 pages, 6 figures, accepted for publication in Ap