Infrared morphology of HII regions

The New GPS Very Large Array survey at 20 cm forms the basis of the search, together with observations obtained with the Spitzer Space Telescope at 8 and 24um and the Herschel Space Telescope at 70um. Objects having ring-like morphologies at 8um and displaying extended emission at 20cm were selected visually.

Emission at 24um having the form of an inner ring or central peak is also observed in the selected objects. A catalog of 99 ring nebulae whose shapes at 8 and 70um are well approximated by ellipses has been compiled. The catalog contains 32 objects whose shapes are close to circular (eccentricities of the fitted ellipses at 8um no greater than 0.6, angular radius exceeding 20").