Resolving the Collimation Zone of an Intermediate-mass Protostellar Jet

We report new VLA and e-MERLIN high-resolution and -sensitivity images of the triple radio continuum source in the Serpens star-forming region. These observations allowed us to perform a deep multifrequency, multiepoch study by exploring the innermost regions (≲100 au) of an intermediate-mass young stellar object for the first time, with a physical resolution of ~15 au. The kinematic analysis of knots recently ejected by the protostar indicates that the jet is undergoing episodic variations in velocity. In addition, our multifrequency images reveal striking characteristics, e.g., a highly collimated ionized stream that would be launched at a radial distance of ~0.4 au from the protostar and a narrow (~28 au wide) ionized cavity that would be excited by the interaction of a wide-angle component with the surrounding toroid of infalling material. In light of these results, we propose the scenario in which both a highly collimated jet and a wide-angle wind coexist as the most plausible to explain our observations, either launched by the X-wind or X-plus-disk-wind mechanism.