Descendants of the first stars: the distinct chemical signature of second-generation stars

Abstract

Extremely metal-poor (EMP) stars in the Milky Way (MW) allow us to infer the properties of their progenitors by comparing their chemical composition to the metal yields of the first supernovae. This method is most powerful when applied to monoenriched stars, i.e. stars that formed from gas that was enriched by only one previous supernova. We present a novel diagnostic to identify this subclass of EMP stars. We model the first generations of star formation semi-analytically, based on dark matter halo merger trees that yield MW-like halos at the present day. Radiative and chemical feedback are included self-consistently and we trace all elements up to zinc. Monoenriched stars account for only ∼ 1% of second generation stars in our fiducial model and we provide an analytical formula for this probability. We also present a novel analytical diagnostic to identify mono-enriched stars, based on the metal yields of the first supernovae. This new diagnostic allows us to derive our main results independently from the specific assumptions made regarding Pop III star formation, and we apply it to a set of observed EMP stars to demonstrate its strengths and limitations. Our results may provide selection criteria for current and future surveys and therefore contribute to a deeper understanding of EMP stars and their progenitors.

Probing the existence of very massive first stars

“…stars formed out from an environment solely imprinted by the first stars (e.g. Hartwig et al 2018 andTakahashi et al 2018b for the PISN). Although our results for the "direct descendants" of PISN, i.e.…”

“…Salvadori et al 2015) or that focus on the build-up of the MW halo (e.g. de Bennassuti et al 2017;Hartwig et al 2018). These models are able to interpret the declining frequency of low-carbon band CEMP stars at increasing [Fe/H] in a cosmological context (see also Cooke & Madau 2014;Bonifacio et al 2015).…”

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326∗

“…Building on these results, we can statistically rule out faint quasi-spherical SNe as the source of metals in HE 1327−2326, as no superposition of yields would produce enough Zn relative to the lighter elements. Enrichment by multiple events can also more broadly be eliminated following the theoretical mono-enrichment classification scheme suggested by Hartwig et al (2018)…”

“…More generally, evidence on the first stars and SNe can be obtained from the chem-ical signatures of surviving low-mass, ultra metal-poor (UMP) stars with [Fe/H] 1 < −4.0 . They likely formed from gas enriched by individual first SNe events whose chemical signature they have retained over billions of years (Frebel & Norris 2015;Hartwig et al 2018).…”

The Pristine survey – IX. CFHT ESPaDOnS spectroscopic analysis of 115 bright metal-poor candidate stars

“…Fragmentation of the early star forming regions has also been predicted (e.g., Schneider et al 2003;Clark et al 2011;Greif 2015;Hirano et al 2015), providing an environment where lower mass (∼ 1 M ) stars could form, which would have much longer lifetimes. These old stars are expected to be metal-poor, having formed from nearly pristine gas, and could be used to trace the chemical elements from the massive (first) stars and their subsequent supernovae (e.g., Frebel & Norris 2015;Salvadori et al 2019;Hartwig et al 2018).…”