Very Large Array and Jansky Very Large Array observations of the compact radio sources in M8

TL;DR

This study uses high-resolution radio observations over 30 years to analyze two compact sources in M8, revealing their emission mechanisms and interactions with stellar winds, with implications for understanding star-forming regions.

Contribution

It provides the first detailed multi-epoch radio analysis of the compact sources in M8, identifying emission mechanisms and wind interactions with high spatial resolution.

Findings

Her 36 SE shows a spectral index suggesting wind interaction regions.

G5.97-1.17 exhibits both thermal and non-thermal emission components.

No significant variability was detected over 30 years.

Abstract

We analyze high-resolution Very Large Array and Jansky Very Large Array continuum observations of the M8 region carried out at several epochs that span a period of 30 yr. Our maps reveal two compact sources. One is associated with Her 36 SE, a possible companion of the O7 luminous massive star Her 36, and the other is associated to G5.97-1.17, whose proplyd nature was previously established. With the analyzed data, we do not find significant time variability in any of these sources. The derived spectral index of $\ge 0.1$ for Her~36 SE, the marginal offset of the radio emission with the previous IR detection and the associated X-ray emission previously reported suggest the presence of an unresolved interaction region between the strong winds of Her~36 and Her~36 SE. This region would produce non-thermal contamination to the global wind emission of Her~36 flattening its spectral index. On the other hand, the emission of G5.97-1.17 can be also explained by a mixture of thermal and non-thermal emission components, with different relative contribution of both emission mechanisms along the proplyd. We argue that the shock created by the photo-evaporation flow of the proplyd with the collimated stellar wind of Her~36 accelerates charged particles in G5.97-1.17 producing considerable synchrotron emission. On the contrary, an electron density enhancement at the southwest of G5.97-1.17 makes the thermal emission dominant over this region.