The symbiotic star AG Dra

Abstract

The results are given of photometric (in the system UBVRJHKLM) and spectrophotometric (in the range 3300-7500 A) observations of the symbiotic star AG Dra. Its cold component is a red giant of the spectral class K4-K5 having approximately constant light, ..delta..I less than or equal to 0/sup m/3, which fills its Roche lobe and is apparently on the asymptotic branch of giants. At wavelength 5 ..mu..m there is an infrared excess associated with the emission of a gas envelop with mass M approx. 10/sup -6/ M/sub circle/. The observations of AG Dra showed that with increasing bolometric flux from the hot component its effective temperature decreases. The hot component may be a red dwarf with M approx. 0.4 M/sub circle/ onto whose equatorial regions there is disk accretion of the matter of the cold star at M greater than or equal to 10/sup -4/ M/sub circle//yr. When the accretion rate is enhanced, during an outburst of AG Dra, the stellar wind from the surface of the red dwarf is increased and its effective temperature decreased. The hot component of AG Dra could also be a white dwarf with L greater than or equal to 3 x 10/sup 3/ L/sub circle/more » and R/sub eff--/ 0.2 R/sub circle/. The energy source of its outbursts is the gravitational energy of matter accreting at the rate M greater than or equal to 10/sup -5/ M/sub circle//yr. At the times between the outbursts, its luminosity may be determined by the release of energy produced by the burning of a hydrogen layer source on its surface.« less