Multi-frequency variations of the Wolf-Rayet system HD193793 (WC7pd+O4-5) III. IUE observations

Details Multi-frequency variations of the Wolf-Rayet system HD193793 (WC7pd+O4-5) III. IUE observations Multi-frequency variations of the Wolf-Rayet system HD193793 (WC7pd+O4-5) III. IUE observations

Sep 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001a%26a...376..460s&link_type=abstract

Astronomy and Astrophysics, v.376, p.460-475 (2001)

Astronomy and Astrophysics

Astrophysics

21

Stars: Binaries: Spectroscopic, Stars: Early-Type, Stars: Wolf-Rayet, Stars: Individual: Wr 140, Stars: Winds, Outflows, Ultraviolet: Stars

Scientific paper

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, omega = 31degr +/- 9degr and KO 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.

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