Research Note

Hα spectropolarimetry of RY Tauri and PX Vulpeculae^*

¹ Observatório Nacional, Rua General José Cristino 77, São Cristovão, 20921-400 Rio de Janeiro, Brazil e-mail: pereyra@on.br
² Departamento de Astronomia, IAG, Universidade de São Paulo, Rua do Matão 1226, São Paulo, SP 05508-900, Brazil

Received: 25 June 2008
Accepted: 17 November 2008

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 in 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 shows a variable Hα double peak in 2004-2005 data. A polarization line effect is evident in the Q-U diagram for both epochs confirming a clockwise rotating disk. A single loop is evident in 2004 changing to a linear excursion plus a loop in 2005. Interestingly, the intrinsic PA calculated using the line effect is consistent between our two epochs (~167°). An alternative intrinsic PA computed from the interstellar polarization-corrected continuum and averaged between 2001-2005 yielded a PA ~ 137°. This last value is closer to perpendicular to the observed disk direction (~25°), as expected from single scattering in an optically thin disk. For PX Vul, we detected spectral variability in Hα along with non-variable continuum polarization when compared with previous data. The Q-U diagram shows a well-defined loop in Hα associated with a counter-clockwise rotating disk. The symmetry axis inferred from the line effect has a PA ~ 91°(with an ambiguity of 90°). 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.