Ha spectropolarimetry of B[e] and Herbig Be stars

Abstract

We present the results of medium resolution ( v 60 km s−1) spectropolarimetric observations across H of a sample of B[e] and Herbig Be objects. A change in linear polarization across H is detected in a large fraction of the objects, with characteristics ranging from simple depolarization in a couple of Herbig Be stars, to more complex behaviour in the probable post main sequence B[e] stars. H in the spectra of HD 37806 and HD 50138 each consist of a double-peaked polarized line and a superposed unpolarized single emission peak, suggesting two distinct line-forming regions.Multiple observations of HD 45677 allow for the separation of electron and dust scattering effects for the first time: the difference between derived intrinsic polarization angles of the two components indicate that the dust-scattering region is clumpy. Two unexpected results are the non-detections of H polarization changes in ! Ori, where depolarization has previously been detected, and in MWC 297, which exhibits source elongation at radio wavelengths. In ! Ori time variability is probably responsible such that this star’s electron-scattering disk was much weakened at the time of observation. Two hypotheses are advanced that might explain the MWC 297 result.