Spectroscopic and photometric studies of the symbiotic star AG Dra.

Spectroscopic and photometric observations in the optical region of the Population II symbiotic star AG Dra were carried out during the period from 1981 to 1985. The spectra show strong emission lines of H I, He I, He II, and the unidentified emission bands at 6830 and 7088 A. The latter two bands may not be due to forbidden lines, because in this star no forbidden lines, except a weak trace of forbidden O III 4363, are seen. In the quiescent stage, equivalent widths of the prominent emission lines were roughly associated with the luminosity in the U band. The observations confirm the spectral type G7 V of the cool component, which is, however, inconsistent with its color corresponding to K3-5 III. This disagreement suggests a metal deficiency in the system. Since 1930, AG Dra has periodically entered in active stages with an interval of about 15 years.