Is super(6) Li in metal-poor halo stars produced in situ by solar-like flares?

• Published in: Astronomy and astrophysics (Berlin) 2007-01, Vol.469 (1), p.265-274
• Main Authors: Tatischeff, V, Thibaud, J-P
• Format: Article
• Language: English
• ISSN: 0004-6361
• DOI: 10.1051/0004-6361:20066635

The high super(6) Li abundances recently measured in metal-poor halo stars are far above the value predicted by Big Bang nucleosynthesis. They cannot be explained by galactic cosmic-ray interactions in the interstellar medium either. Various pre-galactic sources of super(6) Li have been proposed in the literature. We study the possibility that the observed super(6) Li was produced by repeated solar-like flares on the main sequence of these low-metallicity stars. The time-dependent flaring activity of these objects is estimated from the observed evolution of rotation-induced activity in Pop I dwarf stars. As in solar flares, super(6) Li could be mainly created in interactions of flare- accelerated super(3) He with stellar atmospheric super(4) He, via the reaction super(4) He( super(3) He, p) super(6) Li. Stellar dilution and destruction of flare-produced super(6) Li are evaluated from the evolutionary models of metal- poor stars developed by Richard and co-workers. Stellar depletion should be less important for super(6) Li atoms synthesized in flares than for those of protostellar origin. Theoretical frequency distributions of super(6) Li/ super(7) Li ratios are calculated using a Monte-Carlo method and compared with the observations. Excellent agreement is found with the measured super(6) Li/ super(7) Li distribution, when taking into account the contribution of protostellar super(6) Li originating from galactic cosmic-ray nucleosynthesis. We propose as an observational test of the model to seek for a positive correlation between super(6) Li/ super(7) Li and stellar rotation velocity. We also show that the amounts of super(7) Li, Be and B produced in flares of metal-poor halo stars are negligible as compared with the measured abundances of these species. super(6) Li in low-metallicity stars may be a unique evidence of the nuclear processes occuring in stellar flares.