Astronomy and Astrophysics, volume 286, 543-554 (1994/6-2)
Spectral analysis of the planetary nebula K 1-27 and its very hot hydrogen-deficient central star.
RAUCH T., KOEPPEN J. and WERNER K.
Abstract (from CDS):
We present an analysis of the hydrogen-deficient central star of K 1-27 based on NLTE model atmospheres and an analysis of the planetary nebula based on photoionization models. From line profile fits we derive an effective temperature of Teff=100±15kK and a surface gravity of logg=6.5±0.5 for the central star. The atmosphere is dominated by helium while hydrogen cannot be detected (nH/nHe<0.2 by number). We find a nitrogen enrichment (nN/nHe=0.005) but carbon lines are not detected (nC/nHe<0.005). This abundance pattern indicates that the star is a late helium flash object which has lost its hydrogen-rich envelope. The observed abundances may be also affected by element diffusion and radiative levitation. The stellar mass is relatively low (M=0.52+0.06–0.02M☉) 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 stratification 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 took place at the final He flash. In that case He-enrichment in the nebula 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 the first departure from the AGB, it has probably been dispersed.