Rotation of Jets from Young Stars: New Clues from the Hubble Space Telescope Imaging SpectrographD. Coffey, F. Bacciotti, J. Woitas, T. P. Ray & J. Eisloffel2004 ApJ 604 758

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

Introduction(1)ComponentsHigh velocity component ~20-200 km/sLow velocity component ~20 km/sOptical jet ~200 km/sRadio jet ~200 km/sNeutral wind ~200 km/s

Introduction(2)Jets are believed to play an important role in the removal of excess angular momentum from the systemMagnetocentrifugal forces are responsible for jet launchingResolution constraints on observations have impeded progress in validating the magnetocentrifugal mechanismRotation of the jet is predicted

ObservationsObservation were made of the jets associated with TH28, LkH 321, and RW Aur using HST Imaging Spectrograph on 2002 June 22, August 20, October 3, respectivelyAssumption : Inclination angles of 10for TH28, 44for RW Aur and 45for LkH3210.3represents a deprojected distance of ~51, 195 and 233 AU along the jet for TH 28, RW Aur and LkH 321, respectivelyH, [OI], [NII], [SII] lines are usedExposure time 2200 and 2700 s for blue- and redshifted lobes, respectively

General properties of targets (Table 1)

ResultsAll 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 LkH321)Low Velocity Component (LVC) has difference in radial velocities between the two side of the jetHigh Velocity Component (HVC) appears not to be spatially resolved in spectraOffset : set the emission peak in HVC as the jet axis

Position-Velocity contour plotsTH28 [OI] 6300 LkH [SII] 6716 RW Aur [OI] 6300 High Velocity Component is not resolvedJet axis0.10.10.2slice1pixel25km/s0.05

Normalized intensity profiles0.050.150.00.20.250.10.050.150.00.20.1Distance from jet axisGaussian fitting technique, cross-correlation technique velocityError 5 km/s

(Table 3)

Vrad=VNW-VSE for LkH321 (Fig. 2)Error 5 km/s

Vrad=VSW-VNEfor TH 28 (Fig. 3)

Vrad=VNE-VSW for RW Aur (Fig. 4)

Radial velocity (Fig. 5)Clear relation

Derived velocityFrom the results of this spectral analysis, combined with the inclination angles poloidal toroidal red lobe blue lobe RW Aur 144-227 245-288 7-17 TH 28 115-288 230-374 4- 8LkH321 - 540-550 4- 9 km/s

DiscussionObservations 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. 2003Assumption : M*~Msun

ConclusionThe jets show distinct and systematic radial velocity asymmetriesRadial velocity differences in the low velocity component are found to be on the order of 10-25 (5) km/sIn both lobes, jets rotate same directionFoot points are located at 0.3-1.6 AUThese results are consistent with the models of magnetocentrifugal launching

Pixel shift (Table 2)

Anderson et al. 2003Scaling law (conservation)Mestel 1968ZEUS 3D : Axial symmetry : compared with analytic scalingDG Tau foot point ~0.3-4AU

Bacciotti et al. 2000, 2002DG Tau with HST/STIS0.5from the source (110AU when deprojected)Toroidal velocity ~ 6-15 km/sFoot point ~1.8AUV_phi~R^-1Vp_inf=2^1/2(R_a/R0)Vkdot Mjet/Macc=(R_0/R_a)^2~0.1