Proper motions of embedded protostellar jets in Serpens

TL;DR

This study measures the proper motions of protostellar jets in Serpens over a decade, revealing velocity differences between Class 0 and Class I sources and identifying multiple overlapping flows.

Contribution

It provides the first direct measurements of time-variable velocities in a Class 0 jet using multi-epoch proper motion data.

Findings

Proper motions of 31 knots measured over 10 years.

Class 0 jet exhibits higher velocities than Class I jets.

Mass flow rate in Class 0 jet is two orders of magnitude higher.

Abstract

Context. To investigate the dynamical properties of protostellar jets. Aims. 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 $\mu$m line of molecular hydrogen, v=1-0 S(1), obtained with the near-infrared instrument NOTCam over a time-scale of 10 years, are used to determine proper motion of knots and jets. K-band spectroscopy of the brighter knots is used to supply radial velocities, estimate extinction, excitation temperature, and H$_2$ column densities towards these knots. Results. We measure the proper motion of 31 knots over different time scales (2, 4, 6, and 10 years). The typical tangential velocity is around 50 km/s for the 10 year base-line, but for shorter time-scales a maximum tangential velocity up to 300 km/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 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 (dM/dt)$_{\rm out}$ is two orders of magnitude higher in the Class 0 flow than in the two Class I flows.