The symbiotic star CH Cygni. II. The broad Ly alpha emission line explained by shocks

Abstract

Context. In 1985, at the end of the active phase 1977-1986, a broad (4000 km/s) Ly alpha line appeared in the symbiotic system CH Cygni that had never been observed previously. Aims. In this work we investigate the origin of this anomalous broad Ly alpha line. Methods. We suggest a new interpretation of the broad Ly alpha based on the theory of charge transfer reactions between ambient hydrogen atoms and post-shock protons at a strong shock front. Results. We have found that the broad Ly alpha line originated from the blast wave created by the outburst, while the contemporary optical and UV lines arose from the nebula downstream of the expanding shock in the colliding wind scenario.

arXiv comment5 pages, 2 figures, accepted for publication in A&A on 7th April 2008

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• The symbiotic star CH Cygni. I. An analysis of the shocked nebulae at different epochs
• The symbiotic system AG Draconis. Soft X-ray bremsstrahlung from the nebulae
• The symbiotic system Z Andromedae : a spectral analysis of the anomalous 1984-1986 outburst