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

TL;DR

This paper analyzes spectral variability in Z And during its 2006 eruption, proposing a collimated wind model involving a disc-shaped structure that explains diverse spectral line features and their evolution.

Contribution

It introduces a unified model where a disc-shaped structure collimates stellar wind, explaining spectral line variability during the eruption.

Findings

Satellite high-velocity components in Hbeta indicate bipolar outflows.

Spectral line profiles can be explained by a collimated wind model.

Changes in line intensities correlate with eruption phases.

Abstract

High-resolution observations in the region, centered at 4400 \AA\ and those of the lines HeII 4686, Hbeta and HeI 6678 of the spectrum of the symbiotic binary Z And were performed during its outburst in 2006. The line Hbeta 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 HeII 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 NIII and CIII 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.