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NLTE spectral analysis of helium-rich sdO stars from the southern HK survey.
(Astronomical Society of the Pacific, 1996)
We have determined effective temperatures, surface gravities, and helium-to-hydrogen abundance ratios by fitting NLTE model atmospheres to high signal-to-noise- spectra of eight helium-rich sdO stars detected in the southern ...
The planetary nebulae of PG 1159 stars - clues to their evolutionary history
(Astronomical Society of the Pacific, 1996)
It is shown that many planetary nebulae (PN) surrounding PG 1159 stars display a bipolar morphology. The frequency of these nebulae is higher than observed in other PN samples. Implications for the evolutionary history of ...