explored, fundamental physical mechanism in the formation of thefirst stellar objects2which may differ from that for stars more metal-rich than [Fe/H] ¼ 24.0.HE1327–2326 permits exploration of the many formationtheories of the earliest stars proposed for HE0107–5240. One ideais the pre-enrichment of the gas clouds from which the two starsformed by a first generation ‘faint’ type-II supernova (M < 25M()experiencing mixing and fallback3, or rotating, massive objects(M < 200–300M(; ref. 18). In this case, HE1327–2326 would bean early Population II star, formed from gas enriched by one (orpossibly a few) of the first type-II supernovae. In particular, thequantitative predictions of abundance patterns by updatedmodels of ‘faint’ type-II supernovae (N. Iwamoto, H. Umeda,N. Tominaga and K. Maeda, personal communication) agree withthe chemical abundance patterns of HE1327–2326. The diversity ofMg/Fe ratios found in HE1327–2326 and HE0107–5240 is easilyexplained by the variety of mixing and fallback. A remainingproblem is the Sr, whose production is not yet included in thesetype-II supernova models.Another idea is the accretion of heavy elements from theinterstellar medium onto first-generation low-mass stars (Popu-lation III)1,2,19. In this case, however, the high abundances of lighterelements must be explained by other processes. The unevolvedstatus of HE1327–2326 means that the scenario in which internalmixing processes lead to the dredge-up of processed material canbe excluded. A remaining possibility is mass transfer from an AGBstar within a binary system1,5. Mass transfer could naturallyaccount for the Li depletion20found in HE1327–2326. The highSr abundance is problematic, along with the non-detection of Ba,which cannot be explained by the s-process expected to occur inAGB stars. 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