P. W. Hill

Secular contraction in extreme helium stars and the future of V4334 Sgr

Speculative connections have been made between Sakurais Object andother hydrogen-deficient stars, principally the RCB stars and [WC]central stars of planetary nebulae. RCBs have also been postulated as the precursors of extreme helium stars (EHes). The question arises to whether Sakurais Object will evolve down the [WC]-PG1159 evolution track, or the RCB-EHe-HesdO track. From a number of IUE observations, we have measured thesecular contraction rates and pulsation masses of several EHes. These are inconsistent with the predicted contraction rates for helium-shell burning giants produced by a final helium-shell flash (the [WC]-PG1159 track). Although there may be some similarities between Sakurais Object and some RCBs, if the RCB-EHe conection is valid then these must be superficial rather than structural.

The Central Region of the Planetary Nebula A58

We present images and high-resolution spectra of the hydrogen deficient knot at the centre of the old planetary nebula A58. The spectra confirm that this region contains essentially no hydrogen, as previously suspected. Emission lines from the knot are broad (FWHM ~ 180 and 270 km/s for [NII] and [OIII] lines respectively) and are blue-shifted by ~ 100 km/s relative to the systematic velocity.