Ethynyl around the HII regions S255 and S257

TL;DR

This study investigates the distribution and abundance of ethynyl (C2H) around the HII regions S255 and S257, revealing flat abundance profiles near the regions and peaks near young stars, with implications for understanding molecular cloud chemistry.

Contribution

It provides detailed radial profiles of C2H emission and abundance around HII regions, highlighting the spatial variation and relation to star-forming sources.

Findings

C2H abundance is nearly flat near HII regions.

Maximum C2H abundance occurs near stars with emission lines or X-ray emission.

HII regions have neutral walls moving relative to each other.

Abstract

We present the results of the ethynyl (C2H) emission line observations towards the HII regions S255 and S257 and the molecular cloud between them. Radial profiles of line brightness, column density, and abundance of C2H are obtained. We show that the radial profile of the ethynyl abundance is almost flat towards the HII regions and drops by a factor of two towards the molecular cloud. At the same time, we find that the abundance of ethynyl is at maximum towards the point sources in the molecular cloud -- the stars with emission lines or emitting in X-ray. The line profiles are consistent with the assumption that both HII regions have front and back neutral walls that move relative to each other.