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Astron. Astrophys. 331, 224-230 (1998)

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IUE high-resolution observations of the symbiotic star CH Cygni: confirmation of the triple-star model *

A. Skopal ** 1, 2, M.F. Bode 3, H.M. Lloyd 3 and H. Drechsel 1

1 Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstr. 7, D-96049 Bamberg, Germany
2 Astronomický ústav Slovenskej akadémie vied, SK-059 60 Tatranská Lomnica, Slovakia
3 Astrophysics Research Institute, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK

Received 4 August 1997 / Accepted 30 October 1997


We present and analyse ultraviolet high-resolution spectra of CH Cyg taken during the whole period of the International Ultraviolet Exploler (IUE) mission. Our analysis of the observed variation in the line spectrum confirms a triple-star model recently suggested for CH Cyg.

Radial velocities of emission lines, which are subject to eclipse in the symbiotic pair are placed at antiphase to those of the neutral metal absorptions from the infrared/optical spectrum. This is direct evidence for the orbital motion of the hot component in the inner binary of the triple system.

Variation in the line profiles of highly ionized elements and Ly [FORMULA] also supports the triple-star nature of CH Cyg. Fluxes in the SiIV, SiII and AlIII lines decreased considerably during the eclipse. Circumstellar emission in Ly [FORMULA] is produced by the radiation of the hot star. The central part of its profile ([FORMULA] 1216-1220 Å) remains unchanged during the eclipse, it arises at larger distances from the star. This implies that the hot component radiation was, in fact, practically constant during this time, and thus its observed considerable decline had to be caused only by the eclipse. The outer parts of the Ly [FORMULA] profile extend up to [FORMULA] 2 200 km s-1, they are subject to eclipse, and thus reflect a high velocity outflow originating from the central star.

Key words: binaries: symbiotic – stars: individual: CH Cygni – ultraviolet: stars

* Based on observations by the International Ultraviolet Explorer satellite taken at the Villafranca Satellite Tracking Station of the European Space Agency
** Visiting Astronomer, Liverpool John Moores University

Send offprint requests to: A. Skopal

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© European Southern Observatory (ESO) 1998

Online publication: February 4, 1998