Wind Inhomogeneities in Wolf-Rayet Stars. III. Unusual Emission-Line Profile Variations in [FORMULA][F]γ[SUP]2[/SUP][/F][/FORMULA] Velorum

Abstract

We present very high resolution, very high signal-to-noise ratio spectra from the 3.6 m Canada- France-Hawaii telescope for the strong C III j5696 emission line in c2 Velorum, the brightest Wolf-Rayet (WR) star in the sky. From two nights of spectroscopic monitoring, we have detected line pro—le varia- tions (LPVs) in the form of moving emission features (subpeaks) on the broad, ii —at-topped ˇˇ underlying pro—le. We use the working model from the previous paper in this series to study these LPVs in terms of inhomogeneities in the radially expanding stellar wind. A comparison between simulations and the data suggests the variable subpeaks to consist of a superposition of two distinct components: (1) narrow- moving subpeaks with a mean line-of-sight velocity dispersion km s~1, and (2) broad-moving p m ^ 80 subpeaks with km s~1. Both narrow and broad subpeak components are seen to move system- p m ^ 200 atically in a direction from the line center (m 0) toward the line edges. This motion is found to be consistent with a radial wind expansion at a mean acceleration rate m s~2. The narrow a r 13 ^ 3 subpeaks are found to be similar to the stochastic subpeaks seen in the LPVs from several single and long-period binary WR stars. On the other hand, the broad features are reminiscent of the recurrent subpeaks observed in the LPVs from a few peculiar WR stars (HD 4004, HD 191765, and EZ CMa), although in c2 Vel, we —nd no evidence for a recurrent behavior. We investigate the possibility that, in c2 Vel, these broad variable subpeaks arise from the shock-cone region, at the interface where the wind from the WR star collides with that of its O companion. We —nd no convincing evidence to support this hypothesis, although we suspect that there could be a relation between the existence of broad LPV subpeaks and the presence of the more massive O companion.