Abstract
We present high angular resolution ( ∼ 0to z @. hss ''3) Very Large Array observations at 3.5 cm toward the regions of the exciting sources of two Herbig-Haro systems, namely, HH12 in Orion and HH19 in B335. The observations were made at three different epochs to search for possible fast time variations in the sources (on a scale of one week to one month). In HH 212 we detected, averaging the observations of the three epochs, a faint object, at the expected position for the exciting source of the HH system. Comparison with other radio observations indicates that this source exhibits considerable time variation on a scale of years. In B335 we detected at each epoch the source previously reported by other authors and our results suggest that this object, a thermal radio jet, is variable on timescales of a month. We discuss possible explanations for this fast variability.
