On the origin of HE 0107 - 5240 , the most iron deficient star presently known

We show that the ”puzzling” chemical composition observed in the extremely metal poor star HE0107-5240 may be naturally explained by the concurrent pollution of at least two supernovae. In the simplest possible model a supernova of quite low mass (∼ 15 M⊙), underwent a ”normal” explosion and ejected ∼ 0.06 M⊙ of Ni while a second one was massive enough (∼ 35 M⊙) to experience a strong fall back that locked in a compact remnant all the carbon-oxygen core. In a more general scenario, the pristine gas clouds were polluted by one or more supernovae of relatively low mass (less than ∼ 25 M⊙). The successive explosion of a quite massive star experiencing an extended fall back would have largely raised the abundances of the light elements in its close neighborhood. Subject headings: nuclear reactions, nucleosynthesis, abundances – stars: evolution – stars: interiors – stars: supernovae