PHYSICAL CHARACTERISTICS AND CHEMICAL-COMPOSITION OF THE NEBULAR ENVELOPE AROUND RY SCT

The physical conditions in the far away nebular envelope around the interacting binary RY Sct have been investigated, using the high-dispersion spectrograms obtained at the 1,5 m (ESO) and 6 m (SAO) reflectors. The absolute energy distribution from the infrared to far ultraviolet region in the spectrum of RY Sct was derived for that aim. The equivalent widths and the radiative fluxes of emission for some recombination lines (H, He) and forbidden lines (N, O, Ne, S, Fe) are presented. The temperature and the radius of the exciting central star are determined, as well as the electron density and temperature, the geometrical characteristics and chemical abundaices in the disc-shaped nebular envelope surrounding it. Anomalies of the nebular envelope chemical composition have been analysed. It is noted that the observed anomalies (the excess of He, N, and deficiency of O with respect to H) are explained by nuclear reactions of burning H in the CNO cycle. This result may give the explanation of the evolutionary status of the system RY Sct. Apparently the chemical composition of the nebular envelope corresponds to that of the bright BO component which is filling its Roche lobe and losing mass to the nebular envelope.