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 HE 0107-5240 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 Msolar) underwent a 'normal'' explosion and ejected ~0.06 Msolar of 56Ni while a second one was massive enough (~35 Msolar) to experience a strong fallback 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 Msolar). The successive explosion of a quite massive star experiencing an extended fallback would have largely raised the abundances of the light elements in its close neighborhood.