A 2007 photometric study and UV spectral analysis of the Wolf-Rayet binary V444 Cyg

Photometric and spectroscopic characteristics of the WN5+O6 binary system, V444 Cyg, were studied. The Wilson-Devinney (WD) analysis, using new BV observations carried out at the Ankara University Observatory, revealed the masses, radii, and temperatures of the components of the system as M-WR = 10.64M(circle dot), M-O = 24.68 M-circle dot, R-WR = 7.19 R-circle dot, R-O = 6.85 R-circle dot, T-WR = 31 000 K, and T-O = 40 000 K, respectively. It was found that both components had a full spherical geometry, whereas the circumstellar envelope of the WR component had an asymmetric structure. The O-C analysis of the system revealed a period lengthening of 0.139 +/- 0.018 s yr(-1), implying a mass loss rate of 6.76 +/- 0.39) x 10(-6) M(circle dot)yr(-1) for the WR component. Moreover, 106 IUE-NEWSIPS spectra were obtained from NASA's IUE archive for line identification and determination of line profile variability with phase, wind velocities and variability in continuum fluxes. The integrated continuum flux level between 1200-2000 angstrom) showed a mild and regular increase from orbital phase 0.00 up to 0.50 and then a decrease in the same way back to phase 0.00. This is evaluated as the O component making a constant and regular contribution to the system's UV light as the dominant source. The C IV line, originating in the circumstellar envelope, had the highest velocity while N IV line, originating in deeper layers of the envelope, had the lowest velocity. The average radial velocity calculated by using the C IV line wind velocity) was found as 2326 km s(-1). (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim