9,6-Year periodicity of symbiotic nova RT Ser (1909) during the outburst decay from 1940 to 1994

The behavior of the symbiotic nova RT Ser from 1940 to 1994 from photographic observations made at the Gissar Observatory (1940–1978) and BVR-band observations at the Crimean Observatory (1983–1994) is analyzed. The outburst lightcurve shows a linear decline at a rate of 0^m.06 per year. It appears from the nature of the outburst attenuation that the fading, having already lasted about 80 yr, is still continuing. Judging from the color indices, the principal contribution to the visible light from the system is made by a cool, late-type red giant and hot gas the source of which is, as yet, unknown. The photometric variability observed in the BVR bands with a characteristic time of 10 yr is confirmed by photographic observations of 1928–1978. The period determined from all the data is 9.6 yr and is most likely orbital.Translated fromAstrofizika, Vol. 39, No. 1, pp. 31–40, January–March, 1996.