COMPARATIVE STUDY OF A [WC 6] NUCLEUS WITH OTHER EMISSION-LINES NUCLEI OF PLANETARY NEBULAE

Abstract

The central star (CSPN) of the planetary nebula M 1-25 (PN G 4.9+4.9) is classified as a [WC 6] star, the only CSPN of this subclass known at this time. A comparison with the other emission-lines CSPN (the [WC]-class and the 'weak emission-lines stars' or {\em wels}-class) shows that (1) the characteristics of this [WC 6] star fit well inside the main properties of the other [WC] CSPN ; (2) the [WC] CSPN seem to evolve from the [WC 8-11] (latter) to [WC 2-4] (earlier) subclasses, say from dense nebulae with cool stars to more extended nebulae with hot nuclei, as for other CSPN ; (3) on the two-colour IRAS diagram,the [WC] and the {\em wels} CSPN form two different groups : the progenitors of the [WC]-type CSPN seem to be Carbon stars evolving along post-AGB tracks, whereas the {\em wels} CSPN seem to be related to OH/IR stars, some of them having possibly experienced a late helium-flash.