2016A&A...587A..75D

We determine the proper motion of protostellar jets around Class0 and ClassI sources in an active star forming region in Serpens. Multi-epoch deep images in the 2.122 µm line of molecular hydrogen, v=1-0 S(1), obtained with the near-infrared instrument NOTCam on a timescale of 10 years, are used to determine the proper motion of knots and jets. K-band spectroscopy of the brighter knots is used to supply radial velocities, estimate extinction, excitation temperature, and H₂ column densities towards these knots. We measure the proper motion of 31 knots on different timescales (2, 4, 6, 8, and 10 years). The typical tangential velocity is around 50km/s for the 10-year baseline, but for shorter timescales, a maximum tangential velocity up to 300km/s is found for a few knots. Based on morphology, velocity information, and the locations of known protostars, we argue for the existence of at least three partly overlapping and deeply embedded flows, one Class0 flow and two ClassI flows. The multi-epoch proper motion results indicate time-variable velocities of the knots, for the first time directly measured for a Class0 jet. We find in general higher velocities for the Class0 jet than for the two ClassI jets. While the bolometric luminosites of the three driving sources are about equal, the derived mass flow rate (dM/dt)_out is two orders of magnitude higher in the Class0 flow than in the two ClassI flows.