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

Free access article

Issue		A&A Volume 376, Number 2, September II 2001


Page(s)		460 - 475
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20010879

A&A 376, 460-475 (2001)
DOI: 10.1051/0004-6361:20010879

III. IUE observations

D. Y. A. Setia Gunawan^{1, 2, 3}, K. A. van der Hucht², P. M. Williams⁴, H. F. Henrichs⁵, L. Kaper⁵, D. J. Stickland⁶ and W. Wamsteker⁷

¹ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
    e-mail: diah@astro.rug.nl
² Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
³ present address: Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
⁴ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
    e-mail: p.m.williams@roe.ac.uk
⁵ Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
    e-mail: huib;lexk@astro.uva.nl
⁶ Space Science Department, Rutherford Appleton Observatory, Chilton, Didcot, Oxon OX11 OQX, UK
    e-mail: ds@astro1.bnsc.rl.ac.uk
⁷ ESA-IUE Observatory, VILSPA, PO Box 50727, 28080 Madrid, Spain
    e-mail: wwamstek@notes.vilspa.esa.es

(Received 20 February 2001 / Accepted 15 June 2001 )

Abstract
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 $\pm$ 0.05, $\omega$ = 31 $\degr$ $\pm$ 9 $\degr$ and $K_{\rm O star}$ = 25 $\pm$ 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 $\pm$ 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.

Key words: stars: binaries: spectroscopic -- stars: early-type -- stars: Wolf-Rayet -- stars: individual: WR 140 -- stars: winds, outflows -- ultraviolet: stars

Offprint request: K. A. van der Hucht, k.a.van.der.hucht@sron.nl

SIMBAD Objects in preparation

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