The hidden past of Sakurai's object: Stellar properties before the final helium flash

F.Kerber, J.Köppen, M.Roth, S.C.Trager

ABSTRACT We derive the properties of Sakurai's object before its sudden evolutionary change by studying the remnant ionization of the old PN. The star must have had a surface temperature of 98000 +/- 7000 K. For a distance of 1.5 kpc the luminosity should have been 25 +/- 5 L(SUN). The central star thus was highly evolved and had already reached the tip of the white dwarf cooling track. Sakurai's object indeed is an example of a star undergoing a very late helium flash.