New VLA observations of the HH 1-2 region: Evidence for density enhancements moving along the axis of the VLA 1 radio jet

Using the Very Large Array, we have carried out new, sensitive radio contin uum observations at 6 and 3.6 cm of the HH 1-2 region. The comparison betwe en the 6 cm maps made from data taken in 1986.2 and 1992.9 indicates that V LA 1, the exciting source of the HH 1-2 flow, has suffered a morphological change that is attributed to the motion of a symmetric pair of knots along the axis of the radio jet. The proper motion of these knots, that are obser ved within 1 " from the embedded star, are consistent with the values found for optical and near-IR jets several arcseconds away. We tentatively propo se that one of the knots observed in the 1986.2 radio data has emerged out of the heavily obscured region around VLA 1 as a near-infrared knot in the 1998.2 data of Reipurth and coworkers. This result supports the interpretat ion that the knots are formed by intrinsic processes in the acceleration an d collimation of the flow or by shocks caused by a variable jet running int o itself, and not by instabilities or sheer with the surrounding medium. Th e source VLA 3, associated with an H2O maser and powering a molecular outfl ow, also shows morphological changes that we attribute to the turn-on of a new, faint component. Our sensitive 3.6 cm map reveals the presence of a ne w source, VLA 4, that coincides positionally with the infrared source 3 of Reipurth and coworkers. Finally, we derive a proper motion for HH 1F that a grees closely with the optical values. In the case of HH 2 the complexity o f the source hampers a detailed comparison with the optical proper motions.