Symbiotic stars are now understood as strongly interacting binaries with a compact component (thought to be usually a white dwarf), accreting matter from a cool giant companion. They undergo at certain times " activity ", often explained for most symbiotic stars as due to episodes of thermonuclear burning of matter accreted by the white dwarf.
AG Dra, belongs to the class of yellow symbiotic stars (Friedjung, 1988, 1997) having a K type giant component. It is metal underabundant and has a high radial velocity of -140 suggesting that it belongs to the halo population. These have been disagreements about its distance and the luminosities of its stellar components; its cool giant is probably more luminous than a normal class III giant (Huang et al. 1994 and Mikolajewska et al. 1995). A study of photometric observations, which have a much better time coverage than that of spectra, can help to illuminate the physics of this star.
© European Southern Observatory (ESO) 1998
Online publication: June 18, 1998