Long-term coherent variations in the WR system EZ Canis Majoris: the binary scenario revisited

Abstract

An analysis of seven different spectroscopic and eight photometric sets of observations of the WN5 star HD 50896=EZ CMa, distributed over more than 15 years is used to refine the known 3.76 days period. The value of P = 3.7650 +/- 0.0001 d yields variations which have coherent phase-dependence. Although not conclusive, this coherence in the 3.7650 day periodic variations over such a long time revives scenarios in which HD 50896 consists of a binary system, a hypothesis that had been nearly completely discarded over the past few years. A binary scenario is not in contradiction with the presence of a non-spherically symmetric wind distribution or instabilities in the WR star's wind and, in fact, mechanisms such as these are probably responsible for the difficulty in having until now obtained a period which yields coherent variations. The low X-ray fluxes suggest that the possible companion may not be a collapsed object, or that the accretion process is inhibited. Table~3 available in electronic form only at the CDS via anonymous ftp to: cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html