A Pseudodisk Threaded with a Toroidal and Pinched Poloidal Magnetic Field Morphology in the HH 211 Protostellar System

• Published in: The Astrophysical journal 2019-07, Vol.879 (2), p.101
• Main Authors: Lee, Chin-Fei, Kwon, Woojin, Jhan, Kai-Syun, Hirano, Naomi, Hwang, Hsiang-Chih, Lai, Shih-Ping, Ching, Tao-Chung, Rao, Ramprasad, Ho, Paul T. P.
• Format: Article
• Language: English
• Subjects: accretion, accretion disks; Ammonia; Angular momentum; Astrophysics; Braking; Dust; Flattening; ISM: individual objects (HH 211); ISM: jets and outflows; Kinematics; Magnetic fields; Magnetism; Misalignment; Morphology; Polarization; Protostars; Rotating disks; Rotation; stars: formation
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab2458

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°. 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 it can result from an inside-out collapse of an extended envelope detected before in NH3. 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.