The hydrogen and helium lines of the symbiotic binary Z And during its brightening at the end of 2002

TL;DR

This study analyzes high-resolution spectral lines of the symbiotic binary Z And during its 2002 brightening, revealing properties of its accretion disc and stellar wind through line profile analysis.

Contribution

It provides new insights into the structure of the accretion disc and stellar wind in Z And during its brightening by analyzing specific spectral line profiles.

Findings

Hydrogen lines suggest emission mainly from an optically thin accretion disc.

Broad wings of Halpha are influenced by radiation damping and stellar wind.

Outer radius of the accretion disc estimated as 20-50 R_sun.

Abstract

High resolution observations in the region of the lines Halpha, He II 4686 and Hgamma of the spectrum of the symbiotic binary Z And were performed during its small-amplitude brightening at the end of 2002. The profiles of the hydrogen lines were double-peaked. These profiles give a reason to suppose that the lines can be emitted mainly by an optically thin accretion disc. The Halpha line is strongly contaminated by the emission of the envelope, therefore for consideration of accretion disc properties we use the Hgamma line. The Halpha line had broad wings which are supposed to be determined mostly from radiation damping but high velocity stellar wind from the compact object in the system can also contribute to their appearance. The Hgamma line had a broad emission component which is assumed to be emitted mainly from the inner part of the accretion disc. The line He II 4686 had a broad emission component too, but it is supposed to appear in a region of a high velocity stellar wind. The outer radius of the accretion disc can be calculated from the shift between the peaks. Assuming, that the orbit inclination can ranges from 47$^\circ$ to 76$^\circ$, we estimate the outer radius as 20 - 50 R_sun. The behaviour of the observed lines can be considered in the framework of the model proposed for interpretation of the line spectrum during the major 2000 - 2002 brightening of this binary.