EDP Sciences
Free access
Volume 496, Number 3, March IV 2009
Page(s) 759 - 763
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361/20079283
Published online 09 February 2009
A&A 496, 759-763 (2009)
DOI: 10.1051/0004-6361/20079283

The symbiotic star CH Cygni

The broad Ly$\alpha$ emission line explained by shocks
M. Contini1, 2, R. Angeloni1, 2, and P. Rafanelli1

1  Dipartimento di Astronomia, University of Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
    e-mail: [rodolfo.angeloni;piero.rafanelli]@unipd.it
2  School of Physics and Astronomy, Tel-Aviv University, 69978 Tel-Aviv, Israel
    e-mail: contini@post.tau.ac.il

Received 19 December 2007 / Accepted 1 April 2008

Context. In 1985, at the end of the active phase 1977-1986, a broad (4000  $\rm km\,s^{-1}$) 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.

Key words: stars: binaries: symbiotic -- stars: individual: CH Cyg

© ESO 2009