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Register a new userA Pseudodisk Threaded with a Toroidal and Pinched Poloidal Magnetic Field Morphology in the HH 211 Protostellar System
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The HH 211 protostellar system is currently the youngest Class 0 system found with a rotating disk. We have mapped it at ~ 50 au (0.16) resolution, studying its magnetic field morphology with dust polarization in continuum at 232 and 358 GHz and its kinematics in C18O J=2-1 line. A flattened envelope extending out to ~ 400 au from the disk is detected in the continuum and C18O, slightly misaligned with the disk by 8 degree. It is spiraling inwards and expected to transform into a rotating disk at ~ 20 au, consistent with the disk radius estimated before. It appears to have a constant specific angular momentum and itself can result from an inside-out collapse of an extended envelope detected before in NH$_3$. In the flattened envelope, the polarization is mainly due to the magnetically aligned dust grains, inferring a highly pinched poloidal field morphology there. Thus, both the kinematics and field morphology support that the flattened envelope is a pseudodisk formed as the infalling gas is guided by the field lines to the equatorial plane. Interestingly, a point symmetric polarization distribution is also seen in the flattened envelope, implying that the pinched field lines also have a significant toroidal component generated by the rotation. No significant loss of angular momentum and thus no clear magnetic braking are detected in the flattened envelope around the disk probably because of the large misalignment between the axis of the rotation and the axis of the magnetic field in the cloud core.
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HH 211 is a highly collimated jet originating from a nearby young Class 0 protostar. Here is a follow-up study of the jet with our previous observations at unprecedented resolution up to ~ 0.3 in SiO (J=8-7), CO (J=3-2), and SO (N_J=8_9-7_8). SiO, CO, and SO can all be a good tracer of the HH 211 jet, tracing the internal shocks in the jet. Although the emissions of these molecules show roughly the same morphology of the jet, there are detailed differences. In particular, the CO emission traces the jet closer to the source than the SiO and SO emissions. In addition, in the better resolved internal shocks, both the CO and SO emission are seen slightly ahead of the SiO emission. The jet is clearly seen on both sides of the source with more than one cycle of wiggle. The wiggle is reflection-symmetric about the source and can be reasonably fitted by an orbiting source jet model. The best-fit parameters suggest that the source itself could be a very low-mass protobinary with a total mass of ~ 60 M_Jup and a binary separation of ~ 4.6 AU. The abundances of SiO and SO in the gas phase are found to be highly enhanced in the jet as compared to the quiescent molecular clouds, even close to within 300 AU from the source where the dynamical time scale is <10 yrs. The abundance enhancements of these molecules are closely related to the internal shocks. The detected SiO is either the consequence of the release of Si-bearing material from dust grains or of its formation via gas chemistry in the shocks. The SO, on the other hand, seems to form via gas chemistry in the shocks.
HH 211 is a nearby young protostellar system with a highly collimated jet. We have mapped it in 352 GHz continuum, SiO (J=8-7), and HCO+ (J=4-3) emission at up to ~ 0.2 resolution with the Submillimeter Array (SMA). The continuum source is now resolved into two sources, SMM1 and SMM2, with a separation of ~ 84 AU. SMM1 is seen at the center of the jet, probably tracing a (inner) dusty disk around the protostar driving the jet. SMM2 is seen to the southwest of SMM1 and may trace an envelope-disk around a small binary companion. A flattened envelope-disk is seen in HCO+ around SMM1 with a radius of ~ 80 AU perpendicular to the jet axis. Its velocity structure is consistent with a rotation motion and can be fitted with a Keplerian law that yields a mass of ~ 50+-15 Jupiter mass (a mass of a brown dwarf) for the protostar. Thus, the protostar could be the lowest mass source known to have a collimated jet and a rotating flattened envelope-disk. A small-scale (~ 200 AU) low-speed (~ 2 km/s) outflow is seen in HCOP+ around the jet axis extending from the envelope-disk. It seems to rotate in the same direction as the envelope-disk and may carry away part of the angular momentum from the envelope-disk. The jet is seen in SiO close to ~ 100 AU from SMM1. It is seen with a C-shaped bending. It has a transverse width of <~ 40 AU and a velocity of ~ 170+-60 km/s. A possible velocity gradient is seen consistently across its innermost pair of knots, with ~ 0.5 km/s at ~ 10 AU, consistent with the sense of rotation of the envelope-disk. If this gradient is an upper limit of the true rotational gradient of the jet, then the jet carries away a very small amount of angular momentum of ~ 5 AU km/s and thus must be launched from the very inner edge of the disk near the corotation radius.
We present a large-scale view of the magnetic field in the central 2deg * 2deg region of our Galaxy. The polarization of point sources has been measured in the J, H, and Ks bands using the near-infrared polarimetric camera SIRPOL on the 1.4 m telescope IRSF. Comparing the Stokes parameters between high extinction stars and relatively low extinction ones, we obtain polarization originating from magnetically aligned dust grains in the central few-hundred pc of our Galaxy. We find that near the Galactic plane, the magnetic field is almost parallel to the Galactic plane (i.e., toroidal configuration) but at high Galactic latitudes (| b | > 0.4deg), the field is nearly perpendicular to the plane (i.e., poloidal configuration). This is the first detection of a smooth transition of the large-scale magnetic field configuration in this region.
HH 211-mms is one of the youngest Class 0 protostellar systems in Perseus at ~ 235 pc away. We have mapped its central region at up to ~ 7 AU (0.03) resolution. A dusty disk is seen deeply embedded in a flattened envelope, with an intensity jump in dust continuum at ~ 350 GHz. It is nearly edge-on and is almost exactly perpendicular to the jet axis. It has a size of ~ 30 au along the major axis. It is geometrically thick, indicating that the (sub)millimeter light emitting grains have yet to settle to the midplane. Its inner part is expected to have transformed into a Keplerian rotating disk with a radius of ~ 10 au. A rotating disk atmosphere and a compact rotating bipolar outflow are detected in SO. The outflow fans out from the inner disk surfaces and is rotating in the same direction as the flattened envelope, and hence could trace a disk wind carrying away angular momentum from the inner disk. From the rotation of the disk atmosphere, the protostellar mass is estimated to be <~ 50 M_Jup. Together with results from the literature, our result favors a model where the disk radius grows linearly with the protostellar mass, as predicted by models of pre-stellar dense core evolution that asymptotes to an $r^{-1}$ radial profile for both the column density and angular velocity.
We present the results of Very Large Array NH$_{3}$ $(J,K)=(1,1)$ and $(2,2)$ observations of the HH 111/HH 121 protostellar system. HH 111, with a spectacular collimated optical jet, is one of the most well-known Herbig-Haro objects. We report the detection of a new source (NH$_{3}-$S) in the vicinity of HH 111/HH 121 ($sim$0.03 pc from the HH 111 jet source) in two epochs of the ammonia observations. This constitutes the first detection of this source, in a region which has been thoroughly covered previously by both continuum and spectral line interferometric observations. We study the kinematic and physical properties of HH 111 and the newly discovered NH$_{3}-$S. We also use HCO$^{+}$ and HCN $(J=4-3)$ data obtained with the James Clerk Maxwell Telescope and archival Atacama Large Millimeter/submillimeter Array $^{13}$CO, $^{12}$CO, and C$^{18}$O $(J=2-1)$, N$_2$D$^{+}$ $(J=3-2)$, and $^{13}$CS $(J=5-4)$ data to gain insight into the nature of NH$_{3}-$S. The chemical structure of NH$_3-$S shows evidence for selective freeze-out, an inherent characteristic of dense cold cores. The inner part of NH$_3-$S shows subsonic non-thermal velocity dispersions indicating a coherent core, while they increase in the direction of the jets. Archival near- to far-infrared data show no indication of any embedded source in NH$_3-$S. The properties of NH$_3-$S and its location in the infrared dark cloud suggest that it is a starless core located in a turbulent medium with turbulence induced by Herbig-Haro jets and associated outflows. More data is needed to fully understand the physical and chemical properties of NH$_3-$S and if/how its evolution is affected by nearby jets.
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