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We have reevaluated the orbital elements for each pair of the quadruple (W-R+O) + (O+O) stellar system GP Cep and propose new spectral types WN6o/WCE + O3-6, B0: I + B1: V-III. It is shown that there is only one Wolf-Rayet (W-R) star in GP Cep, contrary to a previous claim. A rate of change = 1.3 ± 0.2 s yr-1 is determined for the W-R+O pair, which leads to a new period of 6.6887 days and to a W-R mass-loss rate of (0.8-3.0) × 10-5 M☉ yr-1. Masses for this pair are estimated to be MW-R 6 M☉ and MO 21 M☉. The effects of wind-wind collision in the W-R+O pair are studied. It is shown that even after allowing for dilution by the OB components of the quadruple system, these effects are not as strong as in the binary V444 Cygni (WN5+O6, P = 4.212 days). In GP Cep, the phase-dependent, relatively weak excess emission does not originate in the arms of the bow shock cone. Rather, it emerges from the extra heated portion of the W-R wind facing the hot O companion. The trailing bow shock arm is clearly seen, however, as an enhanced He I absorption component near quadrature at phase ~0.73. An anomalous blueshifted He I absorption is present at phase ~0.9, as is also seen in V444 Cyg, in the WC8+O9 I/O8 III binary γ Velorum and in the LBV-cotype binary R81 (B2.5 Iab:e). A 3.5 day orbit for the eclipsing B star pair is confirmed.

EZ CMa is an apparently unusual Wolf-Rayet star of the nitrogen sequence that exhibits strong variations on a period of 3.77 days with coherency lasting typically about 10 cycles. We have used an extensive set of optical spectroscopic observations to investigate a possible link between its line-profile and photometric continuum variability. Despite the strong epoch dependency of the variations, a persistent correlation is found between changes in the wind line profiles (N V λλ4604, 4620 in particular) and in continuum flux emanating near the stellar core. We suggest that these observations give further support to the idea that the physical conditions prevailing in the vicinity of the star's photosphere have a significant impact on the wind structure and that a spatial dependence of these conditions at the base of the outflow induces the formation of azimuthal wind structures in EZ CMa. The epoch-dependent nature of the variability could be related to long-term behavior of corotating magnetic structures, although pulsational instabilities constitute a viable alternative.

We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMa during 20 consecutive nights in 1995 January in support of the IUE Mega-project. In parallel with this optical spectroscopy, we also monitored EZ CMa using narrowband photometry. The light curve was found to be remarkably stable when folded with the P \ 3.77 day period, and it had a peak-to-valley amplitude of 0.1 mag. The P Cygni absorption components of He I j3889 and He I j5876 display a similar global pattern of variability as was found for the simultaneously acquired UV pro-les. The strengthening of the P Cygni absorption component of these transitions is associated with the maximum of the continuum Nux. Con- versely, the absorption trough of N V j4604 gradually disappears as the star brightens. Although the emission parts of the lines are variable at di†erent levels, they all show the same pattern of variability, which consists of phase-dependent shifts of extra emission components superposed on the pro-les. A strong correlation is found between the continuum-light level and the equivalent width of most transitions. The line skewness and the full-width at half-maximum show a daily recurrence timescale, reNecting the light curve changes. We have addressed in a rigorous statistical way the signi-cance of the variations by calculating the "" temporal variance spectrum.II For any given line, we found enhanced variability at some velocities, although the whole pro-le displays a statistically signi-cant level of varia- bility. Arguments against a compact companion as the cause of the observed periodic variability are present- ed. Instead, our observations strongly support the suggestion in the IUE Mega analysis that the atypical level of variability results from the rotation of a structured wind. We propose that the wind variability of EZ CMa is triggered by photospheric activity, or that the wind is controlled by a large-scale magnetic -eld.