Proper Motions of Young Stellar Outflows in the Mid-Infrared with Spitzer. II. HH 377/Cep E

TL;DR

This study measures the proper motions of young stellar outflows in Cep E using mid-infrared observations, revealing high-velocity molecular hydrogen gas moving along the outflow, supported by hydrodynamical modeling.

Contribution

It provides the first detailed proper motion measurements of Cep E's outflow in the mid-infrared, combining observations with hydrodynamical simulations to understand gas dynamics.

Findings

Outflow lobes have tangential velocities of 62 and 94 km/s.

H2 gas moves at highly supersonic velocities without dissociation.

Model supports the idea of H2 reformation or magnetic shielding in shocks.

Abstract

We have used multiple mid-infrared observations at 4.5 micron obtained with the Infrared Array Camera, of the compact (~1.4 arcmin) young stellar bipolar outflow Cep E to measure the proper motion of its brightest condensations. The images span a period of ~6 yr and have been reprocessed to achieve a higher angular resolution (~0.8 arcsec) than their normal beam (2 arcsec). We found that for a distance of 730 pc, the tangential velocities of the North and South outflow lobes are 62+/-29 and 94+/-6 km/s respectively, and moving away from the central source roughly along the major axis of the flow. A simple 3D hydrodynamical simulation of the H2 gas in a precessing outflow supports this idea. Observations and model confirm that the molecular Hydrogen gas, traced by the pure rotational transitions, moves at highly supersonic velocities without being dissociated. This suggests either a very efficient mechanism to reform H2 molecules along these shocks or the presence of some other mechanism (e.g. strong magnetic field) that shields the H2 gas.