Unveiling the molecular environment of the ring nebula RCW 78

TL;DR

This study investigates the molecular, neutral, and ionized gas around the ring nebula RCW 78, revealing molecular gas detection, star formation activity, and the influence of the WR star HD 117688 on the surrounding environment.

Contribution

It provides new CO observations of RCW 78, identifying molecular gas distribution, star formation activity, and the impact of stellar winds and radiation on the nebula's environment.

Findings

Molecular gas with velocities -56 to -33 km/s detected, mainly in the western region.

Total molecular mass estimated at 1.3 x 10^5 solar masses.

Presence of YSO candidates indicating ongoing star formation.

Abstract

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). We based our study on CO observations carried out with the SEST and NANTEN telescopes. We report the detection of molecular gas with velocities in the range -56 to -33 km/s. The CO emission is mainly connected to the western section, with a total molecular mass of 1.3 x 10^5 solar masses. The analysis of the HI gas distribution reveals the HI envelope of the molecular cloud, while the radio continuum emission shows a ring-like structure, which is the radio counterpart of the optical nebula. The gas distribution is compatible with the western section of RCW 78 having originated in the photodissociation and ionization of the molecular gas by HD 117688, and with the action of the stellar winds of the WR star. A number of infrared point sources classified as YSO candidates showed that stellar formation activity is present in the molecular gas linked to the nebula. The fact that the expansion of the bubble have triggered star formation in this region can not be discarded.