Resolved polarization changes across Halpha in the classical T Tauri star RY Tau

Abstract

We present linear Halpha spectropolarimetry of the classical T Tauri star RY Tau. A change in the polarization percentage and position angle across Halpha 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 (Q,U) diagram and find it to be 146 +/- 3 degrees. This is perpendicular to the position angle of the disc of 48 +/- 5 degrees as deduced from submillimeter imaging by Koerner & Sargent (1995). 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 90 degrees 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.