On the Orbital Period and Models of V Sge

Abstract

The orbital period of V Sge is decreasing at a rate which increased from dP/dt=-(4.11\pm 0.33)\times 10^{-10} in 1962 to -(5.44\pm 0.61)\times 10^{-10} in 2022. This implies that the mass trahsfer from the secondary component is accelerating. From the evidence based on the orbital period variations, combined with estimates of the mass loss from the system based on radio observations, it follows that (1) the mass transfer rate from the secondary component is larger than dM2/dt=-5\times 10^{-6}M{\odot }/yr, possibly as large as dM2/dt=-2.5\times 10^{-5}M{\odot }/yr, and (2) the mass loss rate from the primary component is dM1/dt=-4\times 10^{-7}M{\odot }/yr or larger. Close similarity of V Sge to binary Wolf-Rayet stars supports the model with primary component being a hot, evolved star loosing its mass. Several arguments are presented which exclude the alternative model with primary component being a white dwarf with an accretion disk.