H alpha spectropolarimetry of the Herbig Ae star AB Aurigae

We present spectropolarimetric observations, obtained at H alpha, of the He rbig Ae star AB Aurigae. Changes in linear polarization across the H alpha line probe structure in the immediate circumstellar environment of the cent ral star, down to scales of the order of one to a few stellar radii. In the case of AB Aurigae the observed polarimetric signature is complex. After a pplying a correction for foreground continuum polarization, we find that th ere is a linear-polarized H alpha emission component intrinsic to the sourc e. Rotation of the angle of polarization through the emission-line profile suggests scattering in a rotating circumstellar disc. The magnetic accretor model commonly applied to T Tauri stars shows promise of explaining these data.