Anomalous extinction in the planetary nebula Abell 30.

Abstract

The stellar continuous energy distribution from 8000 to 1250 A in Abell 30 is quite peculiar. The observed flux can be understood if a hot central star (approximately 200,000 K) is immersed in an absorbing dust cloud which has anomalous absorption with its peak near 2470 A. The dust nebula is a strong infrared source, maintained by conversion of the stellar UV flux. The internal reddening is E(B - V) = 0.30 mag and reaches 2.5 mag at 2470 A; it is best matched not by graphite but by laboratory observations of carbon smoke. Intense P Cygni lines show that a strong stellar wind exists. The central star may be an O subdwarf, approaching more nearly a helium-carbon degenerate DO.