Linear polarization in forbidden lines of the T Tauri star RY Tauri

¹ ELT Project Office, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan e-mail: hiroshi.akitaya@nao.ac.jp
² Visiting Astronomer, Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asakuchi, Okayama 719-0232, Japan
³ Photocoding, Higashi-Hashimoto 3-16-8-101, Sagamihara, Kanagawa 229-1104, Japan
⁴ Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
⁵ Nishi-Harima Astronomical Observatory, Sayo-cho, Hyogo 679-5313, Japan
⁶ Department of Science Education, Gunma University, Aramaki, Maebashi, Gunma 371-8510, Japan
⁷ Astronomical Institute, Graduate School of Science, Tohoku University, Aramaki, Aoba, Sendai 980-8578, Japan

Received: 2 November 2008
Accepted: 6 March 2009

Abstract

We performed high-dispersion spectropolarimetry for the T Tauri star RY Tauri and measured linear polarization in seven forbidden lines of [OI]5577, 6300, 6364, [NII]λ6583, [SII]6716, 6731, and [FeII]λ7155. This is the first high-dispersion spectropolarimetry for forbidden lines in T Tauri stars. We successfully detected intrinsic polarization in the [OI]λ6300 line. The intrinsic [OI]λ6300 polarization corrected for the foreground polarization was derived as and , whereas the polarization of the nearby continuum was and . The position angle of [OI]λ6300 polarization is compared with the circumstellar structures found by previous studies. It is nearly perpendicular to the disk long-axis and parallel to the optical H jet. Both the perpendicularity and parallelism potentially suggest relatively axisymmetric distribution of the [OI]λ6300 emitting region and surrounding scattering medium. We constructed a simplified scattering model composed of a point source on a jet axis as an [OI]λ6300 emitter and a flat disk with an inner hole as a scatterer. Applying the observed polarization to the model suggests that the [OI]λ6300 emission emerges close to the central star with a possible separation of less than a few 0.1 AU.