UV Emission line shifts of symbiotic binaries

TL;DR

This study investigates the causes of emission line shifts in symbiotic binaries by analyzing UV spectra, revealing phase-dependent shifts and their possible links to stellar winds and accretion disk occultation.

Contribution

It provides the first detailed analysis of emission line shifts in multiple symbiotic binaries, clarifying their origins and phase variations.

Findings

Resonance and intercombination line shifts vary with orbital phase.

Intercombination lines from more ionised atoms are redshifted.

Line profile effects suggest wind absorption and occultation phenomena.

Abstract

Relative and absolute emission line shifts have been previously found for symbiotic binaries, but their cause was not clear. This work aims to better understand the emission line shifts. Positions of strong emission lines were measured on archival UV spectra of Z And, AG Dra, RW Hya, SY Mus and AX Per and relative shifts between the lines of different ions compared. Profiles of lines of RW Hya and Z And were also examined. The reality of the relative shift between resonance and intercombination lines of several times ionised atoms was clearly shown except for AG Dra. This redshift shows a well defined variation with orbital phase for Z And and RW Hya. In addition the intercombination lines from more ionised atoms and especially OIV are redshifted with respect to those from less ionised atoms. Other effects are seen in the profiles. The resonance-intercombination line shift variation can be explained in quiescence by P Cygni shorter wavelength component absorption, due to the wind of the cool component, which is specially strong in inferior conjunction of this cool giant. The velocity stratification permits absorption of line emission. The relative intercombination line shifts may be connected with varying occultation of line emission near an accretion disk, which is optically thick in the continuum.