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

Abstract

We performed high-dispersion spectropolarimetry for the T Tauri star RY Tauri and measured linear polarization in seven forbidden lines of [OI]λλ5577, 6300, 6364, [NII]λ6583, [SII]λλ6716, 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 p [OI] = 1.17 ± 0.54% and θ [OI] = 107 • ± 13 • , whereas the polarization of the nearby continuum was p cont = 2.4−3.1% and θ cont = 2 • −11 • . 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 Hα 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.

Dynamics of wind and the dusty environments in the accreting T Tauri stars RY Tauri and SU Aurigae

“…Hamann & Persson 1992;Alencar & Basri 2000). Forbidden emission lines of [O i], [N ii], [S ii] and [Fe ii] were observed in the spectrum of RY Tau (Cabrit et al 1990;Akitaya et al 2009). No forbidden lines have been reported for SU Aur.…”

“…In RY Tau the emission spectrum includes Hα, Hβ, the Na i doublet, He i 5876Å, Ca ii doublet and the NIR Ca ii triplet (e.g. Hamann & Persson 1992;Alencar & Basri 2000 (Cabrit et al 1990;Akitaya et al 2009). No forbidden lines have been reported for SU Aur.…”

Photometric, astrometric and polarimetric observations of gravitational microlensing events

“…For example, the emission lines from T-Tauri stars (pre-main sequence stars) show a linear polarization due to the light scattering by dust grains in the circumstellar disk around the central stars. This polarization changes with time due to variations in the configuration of the dust pattern (Drissen et al 1989;Akitaya et al 2009). Schneider & Wagoner (1987) noticed that there is a net and time-dependent polarization for a lensed supernova.…”

Detecting stellar spots through polarimetric observations of microlensing events in caustic-crossing

“…Since, these local polarizations have symmetric orientations with respect to the source center, the net polarization of a distant star is zero. Some effects can break this symmetry and create a net polarization for distant stars such as circum-stellar disk of dust grains around the central star (Drissen et al 1989;Akitaya et al 2009), stellar spots, magnetic field and lensing effect. During a microlensing event, the circular symmetry of source star is broken and result is a net polarization for the source star.…”