A collimated wind interpretation for the spectral variability of Z And during its major 2006 eruption

Abstract

High-resolution observations in the region, centered at $\lambda\,4400~\mathring{\mathrm{A}}$ and those of the lines He ii $\lambda\,4686$, $\mbox{H}\upbeta$ and He i $\lambda\,6678$ of the spectrum of the symbiotic binary Z And were performed during its outburst in 2006. The line $\mbox{H}\upbeta$ had additional satellite high-velocity emission components situated on either side of its central peak. The lines of neutral helium presented two components, consisting of a nebular emission situated close to the reference wavelength and a highly variable P Cyg absorption. Close to the optical maximum the line He ii $\lambda \,4686$ was weak emission feature, but with the fading of the light it changed into an intensive emission consisting of a central narrow component and a broad component with a low intensity. The lines of N iii and C iii were very broadened. We demonstrate that all of these groups of lines with very different profiles can be interpreted in the light of the same model, where a disc-shaped material surrounding the compact object collimates its stellar wind and gives rise to bipolar outflow.