The radio evolution of helium-flash stars

Stars reach the white dwarf phase shortly after the ejection of a planetary nebula, and the termination of hydrogen burning. Around 20% of these stars experience a final helium flash after the cessation of hydrogen burning. In spite of being such a common event, only three cases have ever been observed, largely because of the speed of the subsequent evolution. Because of high extinction, this evolution can only be followed at radio wavelengths. Earlier radio data has shown the onset of circumstellar ionization around Sakurai's Object and V605 Aql, and a compact radio source in CK Vul. We propose new cm observations of all three objects, which will yield the evolution of the temperature of the central stars. This will be used to test current models of explosive helium burning which predict very rapid evolution.