Resolving the circumstellar environment of the Galactic B[e] supergiant star MWC 137 from large to small scales

TL;DR

This study combines multi-wavelength observations to analyze the complex circumstellar environment of the Galactic B[e] supergiant MWC 137, revealing detailed gas and dust structures and dynamics across different scales.

Contribution

It provides a comprehensive multi-scale analysis of MWC 137's circumstellar environment, including a geometrical model and insights into the hot and cold molecular gas distributions.

Findings

Hot CO gas forms a Keplerian disk around the star.

Large amounts of cool molecular gas and warm dust surround the nebula.

Velocity patterns suggest complex nebula kinematics.

Abstract

The Galactic object MWC 137 was suggested to belong to the group of B[e] supergiants. However, with its large-scale optical bipolar ring nebula and the high velocity jet and knots, it is a rather atypical representative of this class. We performed multi-wavelength observations spreading from the optical to the radio regime. Based on optical imaging and long-slit spectroscopic data we found that the northern parts of the large-scale nebula are predominantly blue-shifted, while the southern regions appear mostly red-shifted. We developed a geometrical model consisting of two double-cones. While various observational features can be approximated with such a scenario, the observed velocity pattern is more complex. Using near-infrared integral-field unit spectroscopy we studied the hot molecular gas in the close vicinity of the star. The emission from the hot CO gas arises in a small-scale disk revolving around the star on Keplerian orbits. While the disk itself cannot be spatially resolved, its emission is reflected by dust arranged in arc-like structures and clumps surrounding MWC 137 on small scales. In the radio regime we mapped the cold molecular gas in the outskirts of the optical nebula. We found that large amounts of cool molecular gas and warm dust embrace the optical nebula in the east, south and west. No cold gas or dust were detected in the north and north-western regions. Despite the new insights on the nebula kinematics gained from our studies, the real formation scenario of the large-scale nebula remains an open issue.