Cn 1-1: a peculiar compact planetary nebula.

Cn 1-1 is an emission-line object that shows strong emission lines characteristic of high density planetary nebulae superposed on the stellar spectrum of an F5 III-IV star. The authors estimate the absolute luminosity of the hot star of Cn 1-1 to be L_* ≅ 63 L_sun;. A new estimate of the effective temperature of the star is also made based on the IRAS and IUE data. The position of the star on the HR diagram is discrepant with the young age of the nebula as deduced from the high nebular density. In addition to the cool dust at ≅215K there is a second distinct hot dust component at ≅850K that is probably heated by the radiation from the F type star in its neighbourhood, the star being embedded in the cool nebular dust. Cn 1-1 may be a Type I protoplanetary nebula with a massive nucleus (M ⪆ 1.2 M_sun;) evolving in a binary system.