Emission lines in the spectrum of the symbiotic star AG Draconis from 1997 to 2003

• Published in: Astronomy and astrophysics (Berlin) 2004-02, Vol.415 (1), p.273-282
• Main Authors: LEEDJÄRV, L, BURRNEISTER, M, MIKOŁAJEWSKI, M, PUSS, A, ANNUK, K, GAŁAN, C
• Format: Article
• Language: English
• Subjects: Astronomy; Binary and multiple stars; Cataclysmic binaries (novae, dwarf novae, recurrent novae, and nova-like objects). Symbiotic stars; Earth, ocean, space; Exact sciences and technology; Stars
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20034224

The halo symbiotic star AG Dra has been monitored spectroscopically at the Tartu Observatory, Estonia, from September 1997 to March 2003. Altogether 189 spectra are used in the present paper. In addition, photometric U BV ri observations at the Piwnice Observatory, Poland, from March 1996 to May 2003 are presented. Equivalent widths (EW) of the strongest emission lines (H alpha , H beta , He II lambda 4686, O VI Raman scattered lambda 6825) appear to be strongly variable, and in general, correlate with the U brightness of the star. No apparent correlation with the orbital motion of the binary system was found, except for H beta in the quiescent state. At the same time, there is a clear convergence of the high values of EW to certain phases according to the shorter photometric period (378.5 days) proposed by Bastian (1998) and the pulsational period of the cool giant (355.27 days) by Galis et al. (1999). Higher resolution spectra show variability of the H alpha profiles, with weak absorption component on the blue wing of the line around photometric minimum if the star is in quiescent state. The significant role of the cool giant in the activity of AG Dra is discussed.