PFP 1: A Large Annular Planetary Nebula Caught in the First Stages of   ISM Interaction
  This paper presents (H-alpha + [NII]) imaging and spectroscopy of a previously unknown, highly evolved planetary nebula of low excitation. It was discovered serendipitously from AAO/UKST H-alpha Survey images as part of a project to exploit the survey data and has evaded detection by previous surveys due to very low surface brightness. It is a remarkably annular planetary nebula, some 19' across, making it one of the largest examples of its type. We estimate a radius of 1.5 pc and a distance of 550pc as derived from a new H-alpha surface brightness - radius relation. PFP 1 has near perfect circular symmetry, broken only at the NW edge which is coupled with significantly increased (H-alpha + [NII]) intensity. This indicates an early stage of an interaction with the interstellar medium. A blue central star candidate has been identified from the SuperCOSMOS Sky Survey data. 
M. J. Pierce, D. J. Frew, Q. A. Parker