The velocity structure of the cometary H II regions G13.87+0.28, G32.80+ 0.19B, and G61,48+0.09B1

Abstract

We present H92alpha radio recombination line and radio continuum observations toward three cometary-like H II regions, G13.87 + 0.28, G32.80 + 0.19B, and G61.48 + 0.09B1, with an angular resolution of approximately 2''. The kinematics (H92alpha velocity and line-width fields) and morphology (continuum maps) of the ionized gas from two of these sources, G32.80 + 0.19B and G61.48 + 0.09B1, are best explained by models in which the ionized gas is expanding in an anisotropic medium (champagne models), whereas that of G13.87 + 0.28 can be well explained in terms of a bow shock formed by the stellar wind of a massive star moving supersonically through a molecular cloud.

As predicted theoretically, we find that at the frequency of the H92alpha line non-LTE effects are significant, particularly for the compact, high emission measure H II regions we detected in the direction of two cometary regions.