Photometric and Spectroscopic Variations of the Symbiotic Star EG Andromedae

Abstract

EG And is a symbiotic binary system. The cool component is an M3 III star, the hot one is a subdwarf with temperature 60 250 K and luminosity 1.45 L» (Boyarchuk, 1985). The eclipsing nature of the system suggested from UV spectroscopy by Oliversen et al. (1985) was confirmed photometrically by . The circular spectroscopic orbit of cool component determined by Oliversen et al._Xl985) supposing the orbital period 470 days leads to f(m) « 3.2x10~ M g and detached.configuration.The UBV photometry of EG And was obtained in 1985-87 by 0.6 m telescope at Skalnate" Pleso Observatory. The differential photometry Am = m(EG And) -m(HD 3914) in U colour is presented in Pig. 1. Our observations cover two recent minima, which occured in 1985 and 1986-87. The eclipse is most pronounced in U colour. The details about UBV photoelectric observations of EG And are in the paper of , where orbital period 480 days was suggested. The phase in Pig. 1 was computed using the period 481.7 days, which we obtained from spectroscopic observations. Therefore a new ephemeris for minima is:JD . -2 446 336.7 + 481.7 days x E .(1) min As it is possible to see on Pig. 1, the descending branch of the minimum is steeper than the ascending one, that could be caused by an elliptical orbit. This conclusion has been confirmed from spectroscopic elements.The spectroscopic observations of EG And have been carried out at Asiago Astrophysical Observatory in 1966-69, 1972, 1978, 1983. Altogether 20 spectra were obtained by 1.22 m telescope with a prism spectrograph with dispersion of 6 nm/mm at Ha-. Two spectra with a dispersion 1.8 nm/mm were obtained by 2m telescope at Ondrejov Observatory in 1976, two spectra with the same dispersion were obtained by 0.9m telescope at Torun Observatory in 1986. We measured radial velocities of neutral metals to obtain information about the motion of cool component. The data are presented in Pig. 2, where also the 289