EVIDENCE FOR A BIPOLAR GEOMETRY IN R-CORONAE-BOREALIS

The R Coronae Borealis (RCB) stars produce dust at irregular intervals , but the distribution of the circumstellar material is not known. We report spectropolarimetry of R Coronae Borealis (R CrB) itself, obtain ed in a deep decline with the Wisconsin-Indiana-Yale-NOAO telescope. T he continuum is polarized similar to 1% in the red, rising to similar to 2% in the blue. There are significant polarization variations acros s the emission lines. The polarization of the Na I D lines indicates t hat light from the emission-line region is scattered but at a differen t angle from the stellar continuum. The position angle of the continuu m polarization is almost constant from 1 mu m to 7000 Angstrom but the n changes rapidly, rotating by similar to 60 degrees between 7000 and 4000 Angstrom. This behavior is strikingly similar to that produced in post-asymptotic giant branch (AGB) stars having an obscuring torus an d bipolar dust lobes. These new data strengthen the earlier suggestion that there is a preferred direction to the dust ejections in R CrB. D ust ejections seem to occur predominantly along two roughly orthogonal directions consistent with a bipolar geometry. If confirmed, this fin ding will reinforce the relationship between the RCB stars and other p ost-AGB stars.