Proper motions of embedded protostellar jets in Serpens

Aims: We determine the proper motion of protostellar jets around Class 0 and Class I sources in an active star forming region in Serpens.

Methods: 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.

Results: We measure the proper motion of 31 knots on different timescales (2, 4, 6, 8, and 10 years). The typical tangential velocity is around 50 km s^-1 for the 10-year baseline, but for shorter timescales, a maximum tangential velocity up to 300 km s^-1 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 Class 0 flow and two Class I flows. The multi-epoch proper motion results indicate time-variable velocities of the knots, for the first time directly measured for a Class 0 jet. We find in general higher velocities for the Class 0 jet than for the two Class I jets. While the bolometric luminosites of the three driving sources are about equal, the derived mass flow rate Ṁ_out is two orders of magnitude higher in the Class 0 flow than in the two Class I flows.