Rotation of Jets from Young Stars: New Clues from the Hubble Space Telescope Imaging Spectrograph

1. 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 2004 ApJ 604 758

2. 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

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

4. 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

5. 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 LkHα321 • 0.3″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

6. General properties of targets (Table 1)

7. 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

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

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

10. (Table 3)

11. ΔVrad=VNW-VSE for LkHα321 (Fig. 2) Error ±5 km/s

12. ΔVrad=VSW-VNEfor TH 28 (Fig. 3)

13. ΔVrad=VNE-VSW for RW Aur (Fig. 4)

14. Radial velocity (Fig. 5) Clear relation

15. Derived velocity • From 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- 8 • LkHα321 - 540-550 4- 9 km/s

16. 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)

17. Launching point (Table 4) Anderson et al. 2003 Assumption : M*~Msun

18. 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 10-25 (±5) km/s • In both lobes, jets rotate same direction • Foot points are located at 0.3-1.6 AU • These results are consistent with the models of magnetocentrifugal launching

19. おわり

20. Pixel shift (Table 2)

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

22. 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