D. J. Stickland

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

The colliding-wind binary system WR140 (HD193793, 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, w=31 degrees +/- 9 degrees 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, CIV 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 out ow 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.

IUE Observations of the WN-C Star HD 62910

We have obtained low resolution UV spectrophotometry of the WN-C star HD 62910 in both the SWP (λλ1150–2000) and LWR (λλ1850–3250) IUE spectrographs, and also for HD 117688, WN6, used for comparison. The UV spectrum of HD 62910 is shown in Fig 1 and is seen to be dominated by many strong emission lines, which by comparison with the IUE spectra of other galactic WR stars (Nussbaumer et al. 1981) is found to reflect a predominantly WN-type spectrum, but in addition, weaker features characteristic of WC spectra are also seen, particularly in the LWR wavelength range. In Table 1 we list the principal observed WN and WC features in HD 62910. A comparison of the relative strengths of the WN emissions with those observed in various WN subtypes (Nussbaumer et al. 1981) and with our spectra of HD 117688 confirms the subtype of HD 62910 as WN6 as inferred in the visible (Smith 1968, Van der Hucht et al. 1981).

The Peculiar Binary System HD 45166 (SdO+B8V?)

Although clearly a peculiar object (Anger 1933), HD 45166 has been the subject of remarkably few published optical studies. Heap & Aller (1978, HA) discuss its optical spectrum and give evidence that the object is a binary system comprising a B8v star and a hotter WR-like object, denoted qWR by van Blerkom (1978). This paper presents the first UV observations of the system obtained with IUE at the epochs listed in Table 1. These new data show drastic line (but not apparently continuum) variations with epoch, which cast doubt on the WR-connection, although herein we still adopt the notation “qWR”.