EDP Sciences
Free access
Volume 499, Number 1, May III 2009
Page(s) 163 - 173
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361/200811275
Published online 19 March 2009
A&A 499, 163-173 (2009)
DOI: 10.1051/0004-6361/200811275

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

H. Akitaya1, 2, Y. Ikeda3, K. S. Kawabata4, K. Matsuda5, A. Okazaki6, and M. Seki7

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

We performed high-dispersion spectropolarimetry for the T Tauri star and measured linear polarization in seven forbidden lines of [OI] $\lambda\lambda$5577, 6300, 6364, [NII]$\lambda$6583, [SII] $\lambda\lambda$6716, 6731, and [FeII]$\lambda$7155. This is the first high-dispersion spectropolarimetry for forbidden lines in T Tauri stars. We successfully detected intrinsic polarization in the [OI]$\lambda$6300 line. The intrinsic [OI]$\lambda$6300 polarization corrected for the foreground polarization was derived as $p_\mathrm{[OI]}=1.17\pm 0.54\%$ and $\theta_\mathrm{[OI]} = 107\degr\pm 13\degr$, whereas the polarization of the nearby continuum was $p_\mathrm{cont}=2.4{-}3.1\%$ and $\theta_\mathrm{cont}=2\degr{-}11\degr$. The position angle of [OI]$\lambda$6300 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 $\mathrm\alpha$ jet. Both the perpendicularity and parallelism potentially suggest relatively axisymmetric distribution of the [OI]$\lambda$6300 emitting region and surrounding scattering medium. We constructed a simplified scattering model composed of a point source on a jet axis as an [OI]$\lambda$6300 emitter and a flat disk with an inner hole as a scatterer. Applying the observed polarization to the model suggests that the [OI]$\lambda$6300 emission emerges close to the central star with a possible separation of less than a few $\times$0.1 AU.

Key words: stars: pre-main sequence -- circumstellar matter -- polarization -- techniques: polarimetric -- techniques: spectroscopic -- stars: individual: RY Tauri

© ESO 2009