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Abstract: The chemical abundance patterns observed in metal-poor Galactic halo starscontain the signature of the first supernovae, and thus allows us to probe thefirst stars that formed in the universe. We construct a theoretical model forthe early chemical enrichment history of the Milky Way, aiming in particular atthe contribution from pair-instability supernovae PISNe. These are a naturalconsequence of current theoretical models for primordial star formation at thehighest masses. However, no metal-poor star displaying the distinct PISNsignature has yet been observed. We here argue that this apparent absence ofany PISN signature is due to an observational selection effect. Whereas mostsurveys traditionally focus on the most metal-poor stars, we predict that earlyPISN enrichment tends to `overshoot-, reaching enrichment levels of Ca-H ~=-2.5 that would be missed by current searches. We utilize existingobservational data to place constraints on the primordial initial mass functionIMF. The number fraction of PISNe in the primordial stellar population isestimated to be <0.07, or ~< 40% by mass, assuming that metal-free stars havemasses in excess of 10 M sun. We further predict, based on theoreticalestimates for the relative number of PISNe, that the expected fraction ofsecond generation stars below Ca-H=-2 with a dominant i.e., >90%contribution from PISNe is merely ~1e-4 - 5e-4. The corresponding fraction ofstars formed from gas exclusively enriched by PISNe is a factor of ~4 smaller.With the advent of next generation telescopes and new, deeper surveys, weshould be able to test these predictions.

Author: Torgny Karlsson, Jarrett L. Johnson, Volker Bromm

Source: https://arxiv.org/


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