Accretion-disk reflection of the bipolar wind of BI Crucis.

Linear spectropolarimetry of the symbiotic Mira BI Crucis is presented that demonstrates that the object is intrinsically polarized, confirming previous photopolarimetric observations. It is shown that this intrinsic polarization is perpendicular to the object's extended bipolar nebula. The blue wing of the Hα emission line is unpolarized, while the weaker red wing shows significant polarization. We propose that this spectropolarimetric structure is the result of scattering of the fast bipolar wind flux in the collimating accretion disk-the polarized flux is a `reflection' of the bipolar wind. We construct a numerical model of the scattering geometry which demonstrates that this scenario is capable of reproducing the observed spectropolarimetric structure.