Period Change of the Binary System WR+O V444 Cyg: Updated Ephemeris Formula

Abstract

V444 Cyg is a WN5+O6 V eclipsing binary system that exhibits a secular variation in its orbital period due to the loss of matter from the Wolf-Rayet star through its powerful stellar wind. This makes it possible to obtain a dynamical estimate of the WR star mass-loss rate with minimal modeling assumptions. Numerous studies have been published on this topic. Unfortunately, over time, they have accumulated various flaws due to the authors' differing use of previously published light curves. In this paper, we have critically analyzed all published data, added new data obtained by us, and present a table containing all currently known times of the primary minimum, found in a uniform manner and based on independent original data. Using this table, we updated the value of the parameters of the quadratic formula describing the times of the primary minimum. The found rate of orbital period change is $\dot{P} = 0.134\pm 0.003$ s/year, and the corresponding value of the WR star mass-loss rate is $\dot{M}_{\rm WR} = (6.82 \pm 0.26) \times 10^{-6} M_\odot$/year.