The nova-like brightening of Sakurai's object in Sagittarius has been attributed to the final helium-shell flash of a central star of a planetary nebula, that returns the star towards the domain of red giants in the Hertzsprung-Russell diagram (Duerbeck & Benetti 1996). Few stars have been identified with this phase of evolution: examples include FG Sge, V605 Aql, the planetary nebulae Abell 30, Abell 78 and N66. It is expected that a born-again red giant will consume hydrogen and become starkly hydrogen-deficient, helium- and carbon-rich. Low-resolution spectra led Duerbeck and Benetti (1996) to suggest that Sakurai's object is hydrogen-poor. The presence of strong lines of neutral carbon and oxygen was also noted.
Changes of the surface chemical composition may be rapid for born-again AGB stars, as was observed for FG Sge. Sakurai's object offers the prospect of monitoring such secular changes in another born-again candidate. Observations, as reported here, are surely crucial for an improved understanding of the final He-shell flash.
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998