SPECTRAL-ANALYSIS OF THE PLANETARY-NEBULA K-1-27 AND ITS VERY HOT HYDROGEN-DEFICIENT CENTRAL STAR

We present an analysis of the hydrogen-deficient central star of K 1-2 7 based on NLTE model atmospheres and an analysis of the planetary neb ula based on photoionization models. From line profile fits we derive an effective temperature of T(eff) = 100 +/- 15kK and a surface gravit y of log g = 6.5 +/- 0.5 for the central star. The atmosphere is domin ated by helium while hydrogen cannot be detected (n(H)/n(He)< 0.2 by n umber). We find a nitrogen enrichment (n(N)/n(He)=0.005) but carbon li nes are not detected (n(C)/n(He)<0.005). This abundance pattern indica tes that the star is a late helium flash object which has lost its hyd rogen-rich envelope. The observed abundances may be also affected by e lement diffusion and radiative levitation. The stellar mass is relativ ely low (M = 0.52(+0.06/-0.02) M.) and the spectroscopic distance is 1 .3kpc. The high excitation, low density PN has a mass of M/M. = 0.018 +/- 0.5dex and a radius of 0.15pc. Its helium abundance is definitely solar, while the trace elements could also have lower abundances. A st ratification of the He/H abundance ratio in the nebula can be excluded . The kinematical age is about an order of magnitude smaller than the evolutionary age of the central star. We discuss if the PN ejection to ok place at the final He flash. In that case He-enrichment in the nebu la should be expected. However, in contrast to the central star no He enrichment is found in the PN. If a former PN was ejected at all at th e first departure from the AGB, it has probably been dispersed.