Hot Flashers and He Dwarfs in Galactic Globulars

Context. We revisit the evolutionary scenario for Hot Flasher low-mass structures, where mass loss delays the He flash till the initial phases of their White Dwarf cooling sequence. Aims. Our aim has been to test the theoretical results visa -vis different assumptions about the efficiency of mass loss. Methods. To this purpose, we present evolutionary models covering a fine grid of masses, as obtained assuming a single episode of mass loss in a Red Giant model of 0.86 M⊙ with Z=0.0015. Results. We find a reasonable agreement with previous evolutionary investigations, showing that for the given metallicity late Hot Flashers are predicted to cover the mass range M=0.4975 to M= 0.4845 (±0.0005) M⊙, all models igniting the He-flash with a mass of the H-rich envelope as given by Me=0.00050 ±0.00002 M⊙. The ignition mechanism is discussed in some details, showing the occurrence of a bifurcation in the evolutionary history of stellar structures at the lower mass limit for He ignition. Below such a critical mass, the structures miss the He ignition, cooling down as a Hot Flasher-Manqué He White Dwarf. We predict that these structures will cool down, reaching the luminosity logL/L⊙=-1 in a time at the least five times longer than the corresponding cooling time of a normal CO White Dwarf. Conclusions. On very general grounds, one expects that old stellar clusters with a sizeable population of Hot Flasher should likely produce at least a similar amount of slow-cooling He White Dwarfs. According to this result, in a cluster where 20% of Red Giants escape the He burning phase, one expects roughly twice as White Dwarfs than in a normal cluster where all Red Giants undergo their He flash