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.