Figure 1.
Observed ERE for (a) the Red Rectange (from Witt & Boroson 1990); (b) the planetary nebula NGC 7027 (from Furton & Witt 1992); (c) the NGC 2327 reflection nebula (from Gordon, Witt & Friedmann 1998) and (d) the north-western filament of the reflection nebula NGC 7023 (Witt, personal communication, see also Witt et al. 2006). Panels (a)–(c) reproduced by permission of the AAS.