2021ApJ...909...11J

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 = 8₉-7₈) lines at ∼25 au resolution. With these ALMA and previous 2008 Submillimeter Array 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^–1), consistent with previous measurements in the outer jet. At about four 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 subknots. These subknots are interpreted in terms of a variation in the ejection velocity of the jet with a period of ∼4.5 yr, 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.