Spectroscopy of the symbiotic star CH Cygni from 1996 to 2007

TL;DR

This study presents a detailed spectroscopic monitoring of the symbiotic star CH Cygni over 11 years, revealing its variable emission line profiles, possible disk-like structures, and accretion activity correlated with orbital phases.

Contribution

It provides the first long-term optical spectral analysis of CH Cyg, identifying different activity stages and linking spectral changes to orbital and accretion phenomena.

Findings

Detection of double-peaked H alpha profiles indicating possible disk structures.

Increased Balmer line strength during 1999 periastron passage.

No clear eclipse observed during 2001 event.

Abstract

We monitored a set of emission lines in the optical spectra of CH Cyg using the 1.5-m telescope at the Tartu Observatory, Estonia. Most of the spectra were registered in the H alpha region, but other Balmer lines and lines of He, N, O, and Fe were also investigated in terms of their equivalent widths, radial velocities, and absolute fluxes. The spectra indicate different stages that CH Cyg has been through in the course of our observations. During quiescence, the strength of the line profiles changes in opposite phase with the star's luminosity. The H alpha profile becomes double-peaked at times, which may point to the temporary presence of some disk-like structure, but also to absorption in neutral gas surrounding the area of the formation of the emission component. In 1999, when a periastron passage is assumed according to the 5700-day model, the Balmer lines strengthen considerably, as might be expected due to an increase in the accretion rate. The eclipse in 2001, however, is not noticed. At certain episodes, the controversial 756-day period of CH Cyg is seen in our data.