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 continuum observations at 6 and 3.6 cm of the HH 1-2 region. The comparison between the 6 cm maps made from data taken in 1986.2 and 1992.9 indicates that VLA 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 observed within 1 " from the embedded star, are consistent with the values found for optical and near-IR jets several arcseconds away. We tentatively propose 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 interpretation that the knots are formed by intrinsic processes in the acceleration and collimation of the flow or by shocks caused by a variable jet running into itself, and not by instabilities or sheer with the surrounding medium. The source VLA 3, associated with an H2O maser and powering a molecular outflow, 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 new 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 agrees closely with the optical values. In the case of HH 2 the complexity of the source hampers a detailed comparison with the optical proper motions.