The Wolf-Rayet binary V444 Cygni under the spectroscopic microscope. 1: Improved characteristics of the components and their interaction seen in He I

Abstract

A large accumulation of high signal-to-noise, moderate-resolution optical spectra has led to an unprecedented analysis of the radial velocities of emission and absorption lines in the close binary system V444 Cyg (WN 5 + O6 III-V). Improved orbital elements and masses are K<SUB>WR</SUB> = 332.6 +/- 3.0 km/s, K<SUB>O</SUB> = 108.4 +/- 4.7 km/s, a(sin (i)) = 35.8 +/- 0.4 solar radius, e = 0.036 +/- -0.009, M<SUB>WR</SUB>(sin (i))<SUP>3</SUP>) = 8.8 +/- 0.4 solar mass, M<SUB>O</SUB>((sin(i))<SUP>3</SUP>) = 26.3 +/- 1.0 solar mass. With i = 78.7 +/- 0.5 deg from previous studies, these yield a = 38.0 +/- 0.5 solar radius, M<SUB>WR</SUB> = 9.3 +/- 0.5 solar mass, M<SUB>O</SUB> = 27.9 +/- 1.1 solar mass. Other results include (1) the stable presence of short-period pulsations, P approximately equals 0.36 days in the O-C deviations from the W-R orbital curve based on the He II 4686 and 5412 radial velocities; (2) supersynchronous rotation of the O star by a factor approximately 2: v<SUB>e</SUB>(sin (i)) = 215 +/- 13 km/s, (3) sensitivity, especially of the He I 4471, 4922, and 5876 lines, to the presence of a wind-wind collision region in the form of a bow shock around the O star.