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Published online by Cambridge University Press: 12 April 2016
High mass post-main-sequence nebulae are characterised by a set of unusual, and in certain cases extreme physical characteristics, including large outflow velocities (cf. Phillips and Mampaso, 1988a), extremely compact high emission measure cores (Phillips and Mampaso, 1988b), a high incidence of bipolar morphology (Peimbert and Torres Peimbert, 1982), and evidence for anomalously high levels of shock excited H2 S(l) emission towards both the source cores (Phillips et al 1983, 1985) and nebular peripheries (Zuckerman and Gatley, 1988). The large central star masses also predispose these sources to rapid evolution within the H-R plane (perhaps one or two orders of magnitude more rapid than for typical PN (Schonberner 1981, 1983), and the acquisition of stellar temperatures T* > 105 K, giving rise to correspondingly high levels of nebular excitation.