Unveiling the molecular environment of the ring nebula RCW 78

Aims. We present a study of the ionized, neutral atomic, and molecular gas associated with the ring nebula RCW 78 around the WR star HD 117688 (=WR 55) with the aim of analyzing the distribution of the associated gas and investigating its energetics. Methods. We base our study on 12CO(1–0) and 12CO(2–1) observations of the brightest section of the nebula carried out with the SEST telescope with angular resolutions of 45´´ and 22´´, respectively; and on complementary 12CO(1–0) data of a larger area obtained with the NANTEN telescope with an angular resolution of 2$\farcm$ 7, H