New Wolf-Rayet central stars of planetary nebulae identified on the AAO/UKST HαSurvey

Abstract

We have carried out an archival radio, optical and infrared wavelength imaging survey of 44 Bright-Rimmed Clouds (BRCs) using the NRAO/VLA Sky Survey (NVSS) archive, images from the Digitised Sky Survey (DSS) and the Midcourse Space eXperiment (MSX). The data characterise the physical properties of the Ionised Boundary Layer (IBL) of the BRCs. A total of 25 clouds display 20 cm radio continuum emission that is associated with their bright optical rims. The ionising photon flux illuminating these clouds, the ionised gas pressure and the electron density of the IBL are determined. We derive internal molecular pressures for 9 clouds using molecular line data from the literature and compare these pressures to the IBL pressures to determine the pressure balance of the clouds. We find three clouds in which the pressure exerted by their IBLs is much greater than that measured in the internal molecular material. A comparison of external pressures around the remaining clouds to a global mean internal pressure shows that the majority of clouds can be expected to be in pressure equilibrium with their IBLs and hence are likely to be currently shocked by photoionisation shocks. We identify one source which shows 20 cm emission consistent with that of an embedded high-mass YSO and confirm its association with a known infrared stellar cluster. This embedded cluster is shown to contain early-type B stars, implying that at least some BRCs are intimately involved in intermediate to high mass star formation.