Infrared Morphology of Regions of Ionized Hydrogen
  A search for infrared ring nebulae associated with regions of ionized
hydrogen has been carried out. 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 24 $\mu$m and the Herschel Space Telescope at
70 $\mu$m. Objects having ring-like morphologies at 8 $\mu$m and displaying
extended emission at 20 cm were selected visually. Emission at 24 $\mu$m 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 70 $\mu$m 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 8
$\mu$m no greater than 0.6, angular radius exceeding 20). These objects are
promising for comparisons with the results of one-dimensional hydrodynamical
simulations of expanding regions of ionized hydrogen.
