Resolved polarization changes across Hα in the classical T Tauri star RY Tauri

Abstract

We present linear Hα spectropolarimetry of the classical T Tauri star RY Tau. A change in the polarization percentage and position angle across Hα is detected, which suggests that line photons are scattered in a rotating disc. We derive the position angle from the slope of the loop in the diagram and find it to be 146 ± 3o . This is perpendicular to the position angle of the disc of 48 ± 5o as deduced from millimeter imaging by Koerner & Sargent ([CITE]). This finding is consistent, as scattering off the imaged millimeter disc is expected to yield a polarization signature in a direction that is rotated by 90o from this disc. The observed spectropolarimetric behaviour of RY Tau is reminiscent of that seen in a large group of Herbig Ae stars, suggesting a common circumstellar origin of the polarized photons.