1. Spectroscopic behaviour of the symbiotic binary AG Draconis L. Hric 1, L. Leedjärv 2, R. Gális 3, and E. Kundra 1 1 Astronomical Institute, Slovak Academy of Sciences, Tatranská Lomnica 059 60, The Slovak Republic 2 Tartu Observatory, Observatooriumi 1, Tõravere, 61602 Tartumaa, Estonia 3 Institute of Physics, Faculty of Science, P. J. Šafárik University, Park Angelinum 9, Košice 040 01, The Slovak Republic AG Dra is well known bright symbiotic binary with a white dwarf and a pulsating red giant. Long-term photometry and spectroscopy are discussed. In the system of Ag Dra two periods of variability are detected. The longer one around 550 d is connected with orbital motion and the shorter one around 355 d was interpreted in our older paper as pulsation of the red giant. Moreover we found that active stages change distinctively, but the outbursts are repeated with periods from 359 – 375 d. Spectroscopic observations of AG Dra used in the present paper have been carried out on the 1.5-meter telescope at the Tartu Observatory, Estonia. Absolute fluxes in the emission lines of AG Dra together with the U light curve. Dependence of EWs of the emission lines and the U brightness on the orbital phase. Cross-correlation of the U light curves and EWs of the O VI λ 6825 line of AG Dra and Z And. REFERENCES Friedjung M., Gális R., Hric L., Petrík K., 2003, A&A, 400, 595 Gális R., Hric L., Friedjung M., Petrík K., 1999, A&A, 348, 533 Hric L., Gális R., Leedj ä rv L., Burmeister M., Kundra E., 2014, MNRAS, 443, 1103 Leedj ä rv L., Burmeister M., 2012, BaltAst, 21, 131 Leedj ä rv L., Burmeister M., Mikolajewski M., Puss A., Annuk K., Galan C., 2004, A&A, 415, 273 (L04) Mikolajewska J., Kenyon S. J., Mikolajewski M., Garcia M. R., Polidan R. S., 1995, AJ, 109, 1289 The model including a kind of combination nova might be applicable to AG Dra, provided that one could identify a mechanism of the hot outbursts that acts as a trigger for thermonuclear shell flashes after certain time intervals. It is worth to remind that each activity stage of AG Dra during the 20th century has been different from each other (Hric et al. 2014). The stages B, D, E, and F in their designation have a common feature that they start with two strongest (cool) outbursts of comparable amplitude, but the number of following hot outbursts is different in each stage. In addition, in the stages B, E, and F a kind of precursor outburst about 200 − 300 days before the major outburst can be noticed, while this is not evident in the stage D. Stages A and C are rather different from the others, seemingly not containing major (cool) outbursts. Finally, about 40 years of quiescence before the active stage A also requires special explanation. At present, we can conclude that with the help of some trigger mechanism, it is possible to explain the beginnings of active stages in every 12 − 15 years as nova-like thermonuclear shell flashes. All this seems to take place close to some critical threshold as in some cases (active stages A and C) there has been not enough power to ignite additional nuclear reactions, and the follow-up cycles of hot outbursts are different in each activity stage. The first historical photometric observations were dated to the end of the 19th century. During the period (1890–1996), the AG Dra system underwent three phases of activity: the first one between the years 1932 and 1939, the second one between 1949 and 1955 and the third one between 1963 and 1966. In total, we recognized 15 outbursts in this period: seven during the first active phase, six during the second one and two outbursts during the last one.

2. AG Dra is a well-known bright symbiotic binary with a white dwarf and a pulsating red giant. In the system of AG Dra, three periods of variability are detected. - The longer one around 550 d is related to the orbital motion. - We discovered already in last millennium (1999) the shorter one around 355 d and interpreted as pulsations of the red giant. - Finally in 2014 we understood that there is the third period in range from 359 to 375 days. The outbursts in the system are just repeated with this last period. KOLOS 2015, 3th – 5th December 2015