Hot Flashers and He Dwarfs in Galactic Globulars

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. Our aim has been to test the theoretical results vis-a-vis different assumptions about the efficiency of mass loss. 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 Mo with Z=0.0015. 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 Mo, all models igniting the He-flash with a mass of the H-rich envelope as given by about Me=0.00050. 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-Manque' He White Dwarfs We predict that these structures will cool down, reaching the luminosity logL/Lo=-1 in a time at the least five times longer than the corresponding cooling time of a normal CO White Dwarf. 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