V605 Aquilae: The Older Twin of Sakurai's Object

Abstract

New optical spectra have been obtained with VLT/FORS2 of the finalhelium shell flash (FF) star, V605 Aql, which peaked in brightness in1919. New models suggest that this star is experiencing a very latethermal pulse. The evolution to a cool luminous giant and then back to acompact hot star takes place in only a few years. V605 Aql, the centralstar of the planetary nebula (PN) A58, has evolved fromT_{eff}~5000 K in 1921 to ~95,000 K today. There are indicationsthat the new FF star, Sakurai's object (V4334 Sgr), which appeared in1996, is evolving along a similar path. The abundances of Sakurai'sobject today and V605 Aql 80 years ago mimic the hydrogen-deficient RCoronae Borealis (RCB) stars, with 98% He and 1% C. The new spectra showthat V605 Aql has stellar abundances similar to those seen in Wolf-Rayet[WC] central stars of PNe, with ~55% He, and ~40% C. The stellarspectrum of V605 Aql can be seen even though the star is not directlydetected. Therefore, we may be seeing the spectrum in light scatteredaround the edge of a thick torus of dust seen edge-on. In the presentstate of evolution of V605 Aql, we may be seeing the not too distantfuture of Sakurai's object.Based on observations collected at the European Southern Observatory,Chile (proposal 67.D-0405).