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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
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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
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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
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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
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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
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General properties of targets (Table 1)
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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
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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
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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
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(Table 3)
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Vrad=VNW-VSE for LkH321 (Fig. 2)Error 5 km/s
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Vrad=VSW-VNEfor TH 28 (Fig. 3)
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Vrad=VNE-VSW for RW Aur (Fig. 4)
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Radial velocity (Fig. 5)Clear relation
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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
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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)
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Launching point (Table 4)Anderson et al. 2003Assumption :
M*~Msun
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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
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Pixel shift (Table 2)
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Anderson et al. 2003Scaling law (conservation)Mestel 1968ZEUS 3D
: Axial symmetry : compared with analytic scalingDG Tau foot point
~0.3-4AU
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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