# A Highly Collimated Jet from the Red Square Nebula, MWC 922

## TL;DR

This paper reports the discovery of a highly collimated bipolar jet from the B[e] star MWC 922, revealing detailed structure, velocity, and ionization properties, and suggesting external ionization influences and possible association with nearby star-forming regions.

## Contribution

It provides the first detailed imaging and analysis of a collimated jet from MWC 922, including measurements of its extent, velocity, and ionization state, advancing understanding of jet phenomena in B[e] stars.

## Key findings

- The jet extends about 0.15 pc on each side of MWC 922.
- Jet speed estimated at approximately 500 km/s.
- The nebula and jet are externally ionized by ambient radiation.

## Abstract

Deep, narrow-band \Ha\ and 6584 \AA\ [\Nii ] CCD images of the peculiar, infrared excess B[e] star MWC~922 reveal a collimated, bipolar jet orthogonal to the previously detected extended nebula. The jet consists of a pair of $\sim$0.15 pc segments on either side of MWC~922 separated by gaps. The most distant jet segments disappear $\sim$0.6 pc from the star. The northwest beam points to a faint emission-line feature 1.65 pc from MWC~922 that may be a terminal bow shock where the jet rams the ambient medium. The narrow opening-angle of the jet combined with an estimated internal sound speed of $\sim$10 \kms\ implies a jet speed $\sim$500 \kms . The previously detected nebula extends up to 0.6~pc to the southwest of MWC~922 at right angles to the jet and appears to be an extension of the compact, edge-on disk surrounding the star. It points toward the HII region Messier 16 located $\sim$1\degr\ ($\sim$30 pc in projection) to the southwest. This nebula and jet appear to be externally ionized by the ambient Lyman continuum radiation field and have electron densities of n$_e \sim$ 50 to 100 cm$^{-3}$. The southwest nebula and jet have similar surface brightness in \Ha\ and [\Nii ]. Faint 70 $\mu$m emission traces the southwest ejecta that likely originates from $\sim$50 K dust embedded in the photo-ionized plasma which may shadow the dimmer ejecta northeast of MWC~922. MWC~922 may be a massive member of the Serpens OB1 or OB2 associations surrounding Messier 16 and Sh2-54.