Spectroscopic Searches for Evolutionary Orbital Period Changes in WR+OB Binaries: the case of V444 Cyg
Abstract
We present the results of new photometric and spectroscopic observations of WN5+O6 binary V444 Cyg and a detailed analysis of extant spectroscopy and photometry. Using elements of the spectroscopic orbit and assuming e = 0, i = 78 we determined the masses and orbit sizes of the components of V444 Cyg MO6 = 26.4 MSun, MWN5 = 10.7 MSun, aO6 = 10.6 RSun, aWN5 = 26.1 RSun. Based on new and archival light curves and by applying the Hertzsprung method, we improved the photometrical estimate of secular increase rate of the orbital period in V444 Cyg dP/dtph = 0.119+-0.003 s/yr. From the comparison of the new and archival radial velocity curves of V444 Cyg we independently derived the secular orbital period change rate dP/dtsp = 0.147+-0.032 s/yr, in agreement with the photometrical dP/dtph. The obtained secular increase rate of the binary orbital period dP/dt and the mean radii of the components enabled us to estimate the stellar wind mass-loss rate from WR star dM/dtWN5 = -(6.0+-0.4)*10-6 MSun/yr.
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