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SAO244567 is a rare example of a star that allows us to witness stellarevolution in real time. Between 1971 and 1990 it changed from a B-type starinto the hot central star of the Stingray Nebula. This observed rapid heatinghas been a mystery for decades, since it is in strong contradiction with thelow mass of the star and canonical post-asymptotic giant branch (AGB)evolution. We speculated that SAO244567 might have suffered from a late thermalpulse (LTP) and obtained new observations with HST/COS to follow the evolutionof the surface properties of SAO244567 and to verify the LTP hypothesis. Ournon-LTE spectral analysis reveals that the star cooled significantly since 2002and that its envelope is now expanding. Therefore, we conclude that SAO244567is currently on its way back towards the AGB, which strongly supports the LTPhypothesis. A comparison with state-of-the-art LTP evolutionary calculationsshows that these models cannot fully reproduce the evolution of all surfaceparameters simultaneously, pointing out possible shortcomings of stellarevolution models. Thereby, SAO244567 keeps on challenging stellar evolutiontheory and we highly encourage further investigations.

Breaking news from the HST: The central star of the Stingray Nebula is now returning towards the AGB