A Wolf-Rayet nebula in its disruption phase: high-resolution radio observations of PCG 11

Abstract

(abridged abstract) Wolf-Rayet stars have high mass-loss rates and fast stellar winds. Their interaction with circumstellar material from previous evolutionary phases can produce complex nebular morphologies. Hydrodynamic instabilities can fragment wind-swept material, producing condensations, filaments, and gaps that alter the confinement of stellar wind and ionizing radiation. The role of fragmentation in the late evolution and dispersal of WR nebulae remains poorly constrained. PCG 11, with its fragmented morphology and regular scalloped rim, offers an opportunity to investigate these processes. We aim to characterize the structure of PCG 11 and investigate its ring-like morphology and scalloped rim. We constrain its three-dimensional geometry and determine whether the optical fragmentation pattern is also traced by ionized gas. We obtained high-resolution radio continuum images with MeerKAT at 2.6 and 3.1 GHz and ATCA at 5.5 and 9.0 GHz. The radio emission reveals a hollow, equatorially enhanced structure viewed close to its symmetry axis. The images resolve the rim into condensations, low-brightness gaps, and finger-like protrusions. We quantify the fragmentation scale and relate it to the nebular geometry. We also detect an unresolved source coincident with WR 75ab, whose rising radio spectrum is consistent with thermal wind emission. The nebula processes only a small fraction of the stellar ionizing radiation, indicating substantial photon leakage. PCG 11 captures a poorly observed stage in massive-star bubble evolution: the swept-up shell has developed a coherent instability pattern and become fragmented and porous, while remaining dynamically coupled to the stellar wind. It provides a clear view of how fragmentation and erosion reshape the circumstellar environment during a transitional evolutionary phase.