Third Light in the SS 433 System according to UBVRcIc Photometry

Abstract

UBVR_cI_c observations of the microquasar SS 433 from 1980 to 2023 revealed a persistent effect unusual for classical eclipsing binaries. In the phases of maximum accretion disk opening, the depths of the primary and secondary eclipsing minima of the orbital light curve decrease synchronously with increasing wavelength. To explain this effect, we use a model of an eclipsing binary system in which a third non-eclipsed light is present. It is shown that the main source of the third light at a mass loss rate from the system of 10⁻⁴ \({{M}_{ \odot }}\)/yr are the peripheral semi-transparent regions of the supercritical accretion disk, as well as an extended part of the disk wind. The contribution of the non-eclipsed third light increases from 15% in the B filter to 40% in the I_c filter. The spectrum of the third non-eclipsed light in the range of 4000–8000 Å corrected for interstellar absorption can be described by a power law with an exponent in the wavelength scale close to –1. Significant variations in the brightness of the system outside eclipses are associated mainly not with the classical effect of the ellipsoidality of the components, but with variable absorption of light from the components in the common envelope of the system formed by powerful winds of the supercritical accretion disk and the donor star.