Galactic ring nebulae associated with Wolf-rayet stars. I. Introduction and classification.

A list of 15 galactic ring nebulae associated with Wolf-Rayet stars is presented, whose members were chosen so as to ensure that only WR stars are responsible for their excitation. Photographic and kinematic data were used to classify the nebulae according to their formation mechanisms. The types of WR ring nebulae are: (1) shell-structured H II region; (2) amorphous H II region; (3) stellar ejecta; and (4) wind-blown bubble. The stars with which nebulae in these categories are preferentially associated are respectively: (1) WC; (2) late-type WN; (3) WN8; and (4) early-type WN. A probable scheme for the evolution of the stars and the associated ring nebulae is presented, and WR stars with no detectable nebulosity are used as probes to determine the filling factor of the hot, low-density component in the McKee and Ostriker (1977) three-phase model of the interstellar medium.