A Pulsed, Precessing Jet in Cepheus A

TL;DR

This study reveals that the massive star-forming region Cepheus A features a pulsed, precessing jet from HW2, driven by a star-disk system influenced by a companion star, with multiple outflows and interactions observed.

Contribution

It introduces a model of a precessing jet caused by a companion star's inclined orbit, supported by multi-wavelength observations of Cepheus A.

Findings

HW2 drives a pulsed, precessing jet with a 45-degree change in orientation over 10^4 years.

A second outflow from HW3c/d interacts with HW2's flow, producing X-ray and radio emissions.

The system likely formed through disk-assisted capture of a sibling star by HW2.

Abstract

We present near-infrared H2, radio CO, and thermal infrared observations of the nearby massive star-forming region Cepheus A (Cep A). From H2 bow shocks arranged along four distinct jet axes, we infer that the massive protostellar source HW2 drives a pulsed, precessing jet that has changed its orientation by about 45 degrees in roughly 104 years. The current HW2 radio jet represents the most recent event in this time series of eruptions. This scenario is consistent with the recent discovery of a disk around HW2, perpendicular to the current jet orientation, and with the presence of companions at projected distances comparable to the disk radius. We propose that the Cep A system formed by the disk-assisted capture of a sibling star by HW2. We present a numerical model of a 15 M_sun star with a circumstellar disk, orbited by a companion in an inclined, eccentric orbit. Close passages of the companion through or near the disk result in periods of enhanced accretion and mass loss, as well as forced precession of the disk and associated orientation changes in the jet. The observations reveal a second powerful outflow that emerges from radio source HW3c or HW3d. This flow is associated with blueshifted CO emission and a faint H2 bow shock to the east, and with HH 168 to the west. A collision between the flows from HW2 and HW3c/d may be responsible for X-ray and radio continuum emission in Cep A West.