Ethynyl Around the HII Regions S255 and S257

Abstract

We present the results of the ethynyl (C₂H) emission line observations towards the S255 and S257 HII regions 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 ethynyl abundance is at maximum towards the point sources in the molecular cloud—the stars with emission lines or emitting in X-ray. Line profiles are consistent with the assumption that both HII regions have front and back neutral walls those move relative to each other.