Multi-frequency variations of the Wolf-Rayet system HD 193793 (WC7pd+O4-5)

• Published in: Astronomy and astrophysics (Berlin) 2001-09, Vol.376 (2), p.460-475
• Main Authors: Setia Gunawan, D. Y. A., van der Hucht, K. A., Williams, P. M., Henrichs, H. F., Kaper, L., Stickland, D. J., Wamsteker, W.
• Format: Article
• Language: English
• Subjects: outflows; stars: binaries: spectroscopic; stars: early-type; stars: individual: WR 140; stars: winds; stars: Wolf-Rayet; ultraviolet: stars
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20010879

The colliding-wind binary system WR 140 (HD 193793, WC7pd+O4-5, P = 7.94 yr) was monitored in the ultraviolet by IUE from 1979 to 1994 in 35 short-wavelength high-resolution spectra. An absorption-line radial-velocity solution is obtained from the photospheric lines of the O component, by comparison with a single O star. The resulting orbital parameters, e = 0.87 ± 0.05, ω = 31° ± 9° and $K_{\rm O star}$ = 25 ± 15 km s-1, confirm the large eccentricity of the orbit, within the uncertainties of previous optical studies. This brings the weighted mean UV-optical eccentricity to e = 0.85 ± 0.04. Occultation of the O-star light by the WC wind and the WC+O colliding-wind region results into orbital modulation of the P-Cygni profiles of the C ii, C iv and Si iv resonance lines. Near periastron passage, the absorption troughs of those resonance-line profiles increase abruptly in strength and width, followed by a gradual decrease. In particular, near periastron the blue black-edges of the P-Cygni absorption troughs shift to larger outflow velocities. We discuss that the apparently larger wind velocity and velocity dispersion observed at periastron could be explained by four phenomena: (i) geometrical resonance-line eclipse effects being the main cause of the observed UV spectral variability, enhanced by sightline crossing of the turbulent wind-wind collision zone; (ii) the possibility of an orbital-plane enhanced WC7 stellar wind; (iii) possible common-envelope acceleration by the combined WC and O stellar radiation fields; and (iv) possible enhanced radiatively driven mass loss due to tidal stresses, focused along the orbiting line of centers.