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Register a new userA Rotating Protostellar Jet Launched from the Innermost Disk of HH 212
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The central problem in forming a star is the angular momentum in the circumstellar disk which prevents material from falling into the central stellar core. An attractive solution to the angular momentum problem appears to be the ubiquitous (low-velocity and poorly-collimated) molecular outflows and (high-velocity and highly-collimated) protostellar jets accompanying the earliest phase of star formation that remove angular momentum at a range of disk radii. Previous observations suggested that outflowing material carries away the excess angular momentum via magneto-centrifugally driven winds from the surfaces of circumstellar disks down to ~ 10 AU scales, allowing the material in the outer disk to transport to the inner disk. Here we show that highly collimated protostellar jets remove the residual angular momenta at the ~ 0.05 AU scale, enabling the material in the innermost region of the disk to accrete toward the central protostar. This is supported by the rotation of the jet measured down to ~ 10 AU from the protostar in the HH 212 protostellar system. The measurement implies a jet launching radius of ~ 0.05_{-0.02}^{+0.05} AU on the disk, based on the magneto-centrifugal theory of jet production, which connects the properties of the jet measured at large distances to those at its base through energy and angular momentum conservation.
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The recently discovered protostellar jet known as HH212 is beautifully symmetric, with a series of paired shock knots and bow shocks on either side of the exciting source region, IRAS 05413-0104 (Zinnecker et al. 1998). We present VLA ammonia maps of the IRAS 05413-0104 molecular gas envelope in which the protostellar jet source is embedded. We find that the envelope, with mass of 0.2 M(sun) detected by the interferometer, is flattened perpendicular to the jet axis with a FWHM diameter of 12000 AU and an axis ratio of 2:1, as seen in NH3 (1,1) emission. There is a velocity gradient of about 4-5 km sec^-1 pc^-1 across the flattened disk-like core, suggestive of rotation around an axis aligned with the jet. Flux-weighted mean velocities increase smoothly with radius with a roughly constant velocity gradient. In young (Class 0) systems such as HH212, a significant amount of material is still distributed in a large surrounding envelope, and thus the observable kinematics of the system may reflect the less centrally condensed, youthful state of the source and obscuration of central dynamics. The angular momentum of this envelope material may be released from infalling gas through rotation in the HH212 jet, as recent observations suggest (Davis et al. 2000). A blue-shifted wisp or bowl of emitting gas appears to be swept up along the blue side of the outflow, possibly lining the cavity of a wider angle wind around the more collimated shock jet axis. Our ammonia (2,2)/(1,1) ratio map indicates that this very cold core is heated to 14 Kelvin degrees in a centrally condensed area surrounding the jet source. This edge-on core and jet system appears to be young and deeply embedded. This environment, however, is apparently not disrupting the pristine symmetry and collimation of the jet.
HH 212 is one of the well-studied protostellar systems, showing the first vertically resolved disk with a warm atmosphere around the central protostar. Here we report a detection of 9 organic molecules (including newly detected ketene, formic acid, deuterated acetonitrile, methyl formate, and ethanol) in the disk atmosphere, confirming that the disk atmosphere is, for HH 212, the chemically rich component, identified before at a lower resolution as a hot-corino. More importantly, we report the first systematic survey and abundance measurement of organic molecules in the disk atmosphere within $sim$ 40 au of the central protostar. The relative abundances of these molecules are similar to those in the hot corinos around other protostars and in Comet Lovejoy. These molecules can be either (i) originally formed on icy grains and then desorbed into gas phase or (ii) quickly formed in the gas phase using simpler species ejected from the dust mantles. The abundances and spatial distributions of the molecules provide strong constraints on models of their formation and transport in star formation. These molecules are expected to form even more complex organic molecules needed for life and deeper observations are needed to find them.
We present Spitzer (IRAC) images observations and a VLT 2.1micron image of the HH 212 outflow. We find that this outflow has a strong symmetry, with jet/counterjet knot pairs with Delta x less than 1 arcsec position offsets. We deduce that the jet/counterjet knots are ejected with time differences Delta tau_0 approx. 6 yr and velocity differences Delta v_0~ 2 km/s. We also analyze the deviations of the knot positions perpendicular to the outflow axis, and interpret them in terms of a binary orbital motion of the outflow source. Through this model, we deduce a ~0.7M_solar mass for the outflow source, and a separation of ~80 AU between the components of the binary (assuming equal masses for the two components). Finally, using the IRAC data and the VLT 2.1micron image we have measured the proper motion velocities, obtaining values from 50 to 170km/s.
We report new dust polarization results of a nearly edge-on disk in the HH 212 protostellar system, obtained with ALMA at ~ 0.035 (14 au) resolution in continuum at lambda ~ 878 um. Dust polarization is detected within ~ 44 au of the central source, where a rotationally supported disk has formed. The polarized emission forms V-shaped structures opening to the east and probably west arising from the disk surfaces and arm structures further away in the east and west that could be due to potential spiral arms excited in the outer disk. The polarization orientations are mainly parallel to the minor axis of the disk, with some in the western part tilting slightly away from the minor axis to form a concave shape with respect to the center. This tilt of polarization orientations is expected from dust self-scattering, e.g., by 50-75 um grains in a young disk. The polarized intensity and polarization degree both peak near the central source with a small dip at the central source and decrease towards the edges. These decreases of polarized intensity and polarization degree are expected from dichroic extinction by grains aligned by poloidal fields, but may also be consistent with dust self-scattering if the grain size decreases toward the edges. It is possible that both mechanisms are needed to produce the observed dust polarization, suggesting the presence of both grain growth and poloidal fields in the disk.
HH 212 is a Class 0 protostellar system found to host a hamburger-shaped dusty disk with a rotating disk atmosphere and a collimated SiO jet at a distance of ~ 400 pc. Recently, a compact rotating outflow has been detected in SO and SO2 toward the center along the jet axis at ~ 52 au (0.13) resolution. Here we resolve the compact outflow into a small-scale wide-opening rotating outflow shell and a collimated jet, with the observations in the same S-bearing molecules at ~ 16 au (0.04) resolution. The collimated jet is aligned with the SiO jet, tracing the shock interactions in the jet. The wide-opening outflow shell is seen extending out from the inner disk around the SiO jet and has a width of ~ 100 au. It is not only expanding away from the center, but also rotating around the jet axis. The specific angular momentum of the outflow shell is ~ 40 au km/s. Simple modeling of the observed kinematics suggests that the rotating outflow shell can trace either a disk wind or disk material pushed away by an unseen wind from the inner disk or protostar. We also resolve the disk atmosphere in the same S-bearing molecules, confirming the Keplerian rotation there.
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