A 2.3 day periodic variability in the apparently single Wolf-Rayet star WR134: Collapsed companion or rotational modulation?

The apparently single WN 6 type star WR 134 (HD 191765) is distinguished am ong the Wolf-Rayet star population by its strong, presumably cyclical (P ap proximate to 2.3 day) spectral variations. A true periodicity-which is stil l very much debated-would render WR 134 a prime candidate for harboring eit her a collapsed companion or a rotating, large-scale, inhomogeneous outflow . We have carried out an intensive campaign of spectroscopic and photometri c monitoring of WR 134 from 1989 to 1997 in an attempt to reveal the true n ature of this object. This unprecedentedly large data set allows us to conf irm unambiguously the existence of a coherent 2.25 +/- 0.05 day periodicity in the line-profile changes of He II lambda 4686, although the global patt ern of variability is different from one epoch to another. This period is o nly marginally detected in the photometric data set. Assuming the 2.25 day periodic variability to be induced by orbital motion of a collapsed compani on, we develop a simple model that aims to investigate (1) the effect of th is strongly ionizing, accreting companion on the Wolf-Rayet wind structure, and (2) the expected emergent X-ray luminosity. We argue that the predicte d and observed X-ray fluxes can only be matched if the accretion on the col lapsed star is significantly inhibited. Additionally, we performed simulati ons of line-profile variations caused by the orbital revolution of a locali zed, strongly ionized wind cavity surrounding the X-ray source. A reasonabl e fit is achieved between the observed and modeled phase-dependent line pro files of He II lambda 4686. However, the derived size of the photoionized z one substantially exceeds our expectations, given the observed low-level X- ray Aux. Alternatively, we explore rotational modulation of a persistent, l argely anisotropic outflow as the origin of the observed cyclical variabili ty. Although qualitative, this hypothesis leads to greater consistency with the observations.