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

TL;DR

This study provides an updated ephemeris formula for the eclipsing binary system V444 Cyg, accurately measuring its orbital period change and deriving the Wolf-Rayet star's mass-loss rate through a comprehensive analysis of historical and new data.

Contribution

The paper offers a critically analyzed, uniformly processed dataset of primary minima times and an updated quadratic ephemeris formula for V444 Cyg, improving the accuracy of orbital period change measurement.

Findings

Orbital period change rate: 0.134 ± 0.003 s/year

Wolf-Rayet star mass-loss rate: (6.82 ± 0.26) × 10^{-6} M_sun/year

Updated and unified data set of minima times

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.