Simon Jeffery, Armagh Observatory, College Hill, Armagh, BT61
9DG
Speculative connections have been made between Sakurai's Object and other hydrogen-deficient stars, principally the R Coronae Borealis (RCB) stars and [WC] central stars of planetary nebulae. RCBs have also been postulated as the precursors of extreme helium stars (EHes). In all cases, key discriminants of evolution include hydrogen and carbon surface abundance, the presence (or absence) of a planetary nebula, and evolutionary timescales. Following its spectacular expansion, the question arises as to whether Sakurai's Object (and indeed, FG Sge) will evolve down the [WC]-PG1159 evolution track, or the RCB-EHe-HesdO track.
From a seventeen-year baseline of IUE observations, we have measured the secular contraction of several EHes. These are consistent with the predicted contraction rates for helium-shell burning giants with carbon-oxygen degenerate cores such as might be produced by a final helium-shell flash or by the merger of a CO+He white dwarf. Similar rates have been proposed for RCB stars from pulsation period changes.
If the future evolution of Sakurai's Object differs significantly from that observed for EHes and RCBs, other similarities between these stellar remnants must be superficial rather than structural.