Notices to investigation of symbiotic binaries V. Physical parameters derived from UBV magnitudes

In the optical, the spectrum of symbiotic binaries consists of contributions from the cool giant, symbiotic nebula and the hot star. Strong emission lines are superposed on the continuum. In this paper, we introduce a simple method to extract individual components of radiation from photometric UBV magnitudes. We applied the method to classical symbiotic stars AX Per, AG Dra, AG Peg and Z And, the symbiotic novae RR Tel and V1016 Cyg and the classical nova V1974 Cyg during its nebular phase. We estimated the electron temperature and emission measure of the nebula in these systems and the V magnitude of the giant in the symbiotic objects. Our results are in a good agreement with those obtained independently by a precious modelling the UV-IR SED.