Rotation of Jets from Young Stars: New Clues from the Hubble Space Telescope Imaging Spectrograph D. Coffey, F. Bacciotti, J. Woitas, T. P. Ray & J. Eisloffel T. P. Ray & J. Eisloffel 2004 ApJ

Abstract To answer the question. Whether jets from young star rotate? Observation were made of the jets associated with TH28, LkHα 321, and RW Aur using HST Imaging Spectrograph Forbidden emission lines show velocity asymmetry of 10-25(±5) km/s Foot points are located at ~0.5-2 AU, consistent with the models of magnetocentrifugal launching

Introduction(1) Components High velocity component ~ km/s Low velocity component ~20 km/s Optical jet ~200 km/s Radio jet ~200 km/s Neutral wind ~200 km/s

Introduction(2) Jets are believed to play an important role in the removal of excess angular momentum from the system Magnetocentrifugal forces are responsible for jet launching Resolution constraints on observations have impeded progress in validating the magnetocentrifugal mechanism Rotation of the jet is predicted

Observations Observation were made of the jets associated with TH28, LkHα 321, and RW Aur using HST Imaging Spectrograph on 2002 June 22, August 20, October 3, respectively Assumption : Inclination angles of 10°for TH28, 44°for RW Aur and 45°for LkHα ″represents a deprojected distance of ~51, 195 and 233 AU along the jet for TH 28, RW Aur and LkHα 321, respectively Hα, [OI], [NII], [SII] lines are used Exposure time 2200 and 2700 s for blue- and redshifted lobes, respectively

General properties of targets (Table 1)

Results All radial velocities are quoted with respect to the mean heliocentric velocity of the star (+5km/s for TH28, +23 km/s for RW Aur and -7km/s for LkHα321) Low Velocity Component (LVC) has difference in radial velocities between the two side of the jet High Velocity Component (HVC) appears not to be spatially resolved in spectra Offset : set the emission peak in HVC as the jet axis

Position-Velocity contour plots TH28 [OI] λ6300 Å LkHα [SII] λ6716 Å RW Aur [OI] λ6300 Å High Velocity Component is not resolved Jet axis 0.1″ 0.2″ slice 1pixel 25km/s 0.05″

Normalized intensity profiles 0.05″ 0.15″ 0.0″ 0.2″ 0.25″ 0.1″ 0.05″ 0.15″ 0.0″ 0.2″ 0.1″ Distance from jet axis Gaussian fitting technique, cross-correlation technique → velocity Error ±5 km/s

(Table 3)

ΔVrad=V NW -V SE for LkHα321 (Fig. 2) Error ±5 km/s

ΔVrad=V SW -V NE for TH 28 (Fig. 3)

ΔVrad=V NE -V SW for RW Aur (Fig. 4)

Radial velocity (Fig. 5) Clear relation

Derived velocity From the results of this spectral analysis, combined with the inclination angles poloidal toroidal poloidal toroidal red lobe blue lobe red lobe blue lobe RW Aur TH LkHα km/s

Discussion Observations are in line with the observations of the jet from the T Tauri star DG Tau (Bacciotti et al. 2002) Troidal and poloidal velocities have the same ratio as theoretical predictions (Vlahakis et al. 2000)

Launching point (Table 4) Anderson et al Assumption : M * ~Msun

Conclusion The jets show distinct and systematic radial velocity asymmetries Radial velocity differences in the low velocity component are found to be on the order of (±5) km/s In both lobes, jets rotate same direction Foot points are located at AU These results are consistent with the models of magnetocentrifugal launching

おわり

Pixel shift (Table 2)

Anderson et al Scaling law (conservation) –Mestel 1968 ZEUS 3D : Axial symmetry : compared with analytic scaling DG Tau foot point –~0.3-4AU

Bacciotti et al. 2000, 2002 DG Tau with HST/STIS 0.5″from the source (110AU when deprojected) Toroidal velocity ~ 6-15 km/s Foot point ~1.8AU –V_phi~R^-1 –Vp_inf=2^1/2(R_a/R0)Vk –dot Mjet/Macc=(R_0/R_a)^2~0.1