H\alpha spectropolarimetry of RY Tau and PX Vul

TL;DR

This study uses spectropolarimetry to detect rotating disks in T Tauri stars RY Tau and PX Vul, revealing their disk orientations and confirming the compact source origin of emission lines.

Contribution

First spectropolarimetric detection of line effects in RY Tau and PX Vul, providing insights into their disk geometry and rotation.

Findings

RY Tau shows a variable double-peaked Halpha profile and a consistent polarization PA around 167°.

PX Vul exhibits spectral variability with a well-defined loop indicating a counter-clockwise rotating disk.

Line effects confirm the emission line origin in a compact scattering source within a rotating disk.

Abstract

Aims: To detect line effects using spectropolarimetry in order to find evidence of rotating disks and their respective symmetry axes in T Tauri stars. Methods: We used the IAGPOL imaging polarimeter along with the Eucalyptus-IFU to obtain spectropolarimetric measurements of the T Tauri stars RY Tau (two epochs) and PX Vul (one epoch). Evidence of line effects showing a loop on the Q-U diagram favors a compact rather than an extended source for the line photons in a rotating disk. In addition, the polarization position angle (PA) obtained using the line effect can constrain the symmetry axis of the disk. Results: RY Tau shown a variable Halpha double peak on 2004-2005 data. Polarization line effect is evident on the Q-U diagram for both epochs confirming a clockwise rotating disk. A single loop is evident on 2004 changing to a linear excursion plus a loop on 2005. Interestingly, the intrinsic PA calculated using the line effect is consistent between our two epochs (~167deg). An alternative intrinsic PA computed from the interstellar polarization corrected continuum and averaged between 2001-2005 yielded a PA 137deg. This last value is closer to be perpendicular to the observed disk direction (~25deg) as expected by single scattering in an optically thin disk. For PX Vul, we detected spectral variability in Halpha along with non-variable continuum polarization when compared with previous data. The Q-U diagram shows a well-defined loop in Halpha associated to a counter-clockwise rotating disk. The symmetry axis inferred by the line effect has a PA~91deg (with an ambiguity of 90deg). Our results confirm previous evidence that the emission line in T Tauri stars has its origin in a compact source scattered off a rotating accretion disk.