Hot Flashers and He Dwarfs in Galactic Globulars

Abstract

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

6 pages, 5 figures, accepted for publication on A&A

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Cited by in corpus (13)

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• Very low mass white dwarfs with a C-O core
• On the white dwarf cooling sequence of the globular cluster Omega Centauri
• A Re-Evaluation of the Evolved Stars in the Globular Cluster M13
• Evolutionary and pulsation properties of Type II Cepheids
• Stellar lifetime and ultraviolet properties of the old metal-rich Galactic open cluster NGC6791: a pathway to understand the UV upturn of elliptical galaxies
• Pulsational instabilities driven by the $\epsilon$ mechanism in hot pre-horizontal branch stars I. The Hot-Flasher Scenario
• A Robust Test of Evolution near the Tip of the Red Giant Branch and Missing Giants in NGC 2808
• Discovery of a rapidly pulsating subdwarf B star candidate in omega Cen
• The $i$-processes nucleosynthesis during the formation of He-rich hot-subdwarf stars