Spectroscopic searches for evolutionary orbital period changes in WR plus OB binaries: the case of V444 Cyg

We present the results of new photometric and spectroscopic observations of the WN5 + O6 binary V444 Cyg and a detailed analysis of extant spectroscopy and photometry. Using elements of the spectroscopic orbit and assuming e approximate to 0, i approximate to 78 degrees we determined the masses and orbit sizes of the components of V444 Cyg as M-O6 approximate to 26.4 M-circle dot, M-WN5 approximate to 10.7 M-circle dot, a(O6) approximate to 10.6 R-circle dot, a(WN5) approximate to 26.1 R-circle dot. Based on new and archival light curves and using the Hertzsprung method, we improved the photometric estimate of the secular increase rate of the orbital period in V444 Cyg, obtaining (P) over dot(ph) = 0 . 119 +/- 0.003 s yr(-1). From a comparison of the new and archival radial velocity curves of V444 Cyg, we independently derived the secular orbital period change rate as (P) over dot(sp) = 0.147 +/- 0.032 s yr(-1), in agreement with the photometric (P) over dot(ph). The obtained secular increase rate of the binary orbital period (P) over dot and the mean radii of the components enabled us to estimate the stellar wind mass-loss rate from the WR star as (M) over dot(WN5) = -(6.0 +/- 0.4) x 10(-6) M-circle dot yr(-1).

Automated summary

This article presents the results of new photometric and spectroscopic observations of the WN5 + O6 binary V444 Cyg and provides a detailed analysis of existing spectroscopy and photometry. The study determined the masses and orbit sizes of the components of V444 Cyg, as well as estimated the secular increase rate of the orbital period and the stellar wind mass-loss rate from the WR star.