THE CONTINUUM STRUCTURE OF 11 GALACTIC H-II REGIONS

As a consequence of a program to determine the abundance of He-3 in th e interstellar medium, the continuum structure of 11 Galactic H II reg ions is investigated using radio observations at 8.7 GHz using the VLA and the MPIR 100 m telescope. Accurate He-3 abundance determinations require models for the source structure. The VLA data probe the compac t structures, while the 100 m telescope data measure extended emission not detected by the VLA. In this analysis we characterize H II region structure as being composed of a core-halo geometry. Core properties are derived from the VLA continuum maps, while the halo parameters are set by the 100 m data. For many sources multiple cores are observed. Three models are derived for each H II region. The first two models ar e based on a particular component geometry: a homogeneous sphere and a spherical Gaussian, respectively. The third model uses peak propertie s in the continuum intensity map to derive various physical parameters . A comparison between the three models shows no systematic difference s in the derived electron density and emission measure for the individ ual components. Overall, the scatter between modeled parameters is 15% .