HH 211 is a highly collimated jet with a chain of knots and a wiggle structure on both sides of a young Class 0 protostar. We used two epochs of Atacama Large Millimeter/submillimeter Array (ALMA) data to study its inner jet in the CO(J=3-2), SiO(J=8-7), and SO(N_J=8_9-7_8) lines at ∼25 AU resolution. With these ALMA and previous 2008 Submillimeter Array (SMA) data, the proper motion of 8 knots within ∼250 AU of the central source is found to be ∼0.068" per year (∼102 km/s), consistent with previous measurements in the outer jet. At ∼4 times higher resolution, the reflection-symmetric wiggle can be still fitted by a previously proposed orbiting jet source model. Previously detected continuous structures in the inner jet are now resolved, containing at least 5 sub-knots. These sub-knots are interpreted in terms of a variation in the ejection velocity of the jet with a period of ∼4.5 years, shorter than that of the outer knots. In addition, backward and forward shocks are resolved in a fully-formed knot, BK3, and signatures of internal working surface and sideways ejection are identified in Position-Velocity diagrams. In this knot, low-density SO and CO layers are surrounded by a high-density SiO layer.
@article{arxiv.2012.15057,
title = {25 AU Angular Resolution Observations of HH 211 with ALMA : Jet Properties and Shock Structures in SiO, CO, and SO},
author = {Kai-Syun Jhan and Chin-Fei Lee},
journal= {arXiv preprint arXiv:2012.15057},
year = {2021}
}