Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind

Fast rotating Wolf-Rayet stars are expected to be progenitors of long duration gamma-ray bursts. However, the observational test this model is problematic. Spectral lines originate in expanding stellar wind, therefore a reliable spectroscopical determination their rotational velocities difficult. Intrinsic polarization due modulation wind may provide an indirect way determine these stars. detailed models required for purpose. We intrinsic from hydrodynamical as function velocity. used 2.5D simulations calculate structure winds The account deformation surface rotation, gravity darkening, and nonradial forces. From derived models, we calculated polarization. mass loss rate was scaled take realistic densities into account. predict prolate structure, which leads relatively low level Even large allowed by constrains. obtained similiar that previously optically thin winds. Derived upper limits studied not conflict with bursts