Search for: All records

Abstract Low-metallicity stars preserve the signatures of the first stellar nucleosynthesis events in the Galaxy, as their surface abundances reflect the composition of the interstellar medium from the time when they were born. Aside from primordial Big Bang nucleosynthesis, massive stars, due to their short lifetimes, dominate the wind and explosive ejecta into the interstellar medium of the early Galaxy. Most of them will end as core-collapse supernova (CCSN) explosions, and typical ejected abundance distributions, e.g. in terms of the$$\alpha $$ $\alpha$ -element-to-Fe ratios, reflect these contributions. Essentially all CCSNe contribute⁵⁶Fe (decaying from radioactive⁵⁶Ni). Therefore, low-metallicity stars can be used to test whether the abundances of any other elements are correlated with those of Fe, i.e. whether these elements have been co-produced in the progenitor sources or if they require either a different or additional astrophysical origin(s). The present analysis focuses on stars with [Fe/H]<-2, as they probe the earliest formation phase of the Galaxy when only one or very few nucleosynthesis events had contributed their ejecta to the gas from which the lowest metallicity stars form. This was also the era before low and intermediate mass stars (or type Ia supernovae) could contribute any additional heavy elements. Following earlier work on the origin of heavy r-process elements [1], we extend the present study to examine Pearson and Spearman correlations of Fe with Li, Be, C, N, O, Na, Mg, Si, S, K, Ca, Ti, Cr, Ni, Zn, Ge, Se, Sr, Y, Zr, Mo, Ba, La, Ce, Sm, Eu, Gd, Dy, Yb, Lu, Hf, Os, Ir, Pb, and Th, using high-resolution stellar abundance data from the SAGA [2] and JINA [3] databases. The main goal is to identify which of the observed elements (i) may have been co-produced with Fe in (possibly a variety of) CCSNe, and which elements require (ii) either a completely different, or (iii) at least an additional astrophysical origin. 

Various nucleosynthesis studies have pointed out that the rapid neutron capture r-process elements in very metal-poor (VMP) halo stars might have different origins. It has been known that an r-process can either be obtained in neutron-rich low Ye conditions or in high entropy environments [see e.g. 1–5], an overview over many investigations has appeared recently [6]. In the present article we analyze with statistical methods the observational abundance patterns from trans-Fe elements up to the actinides and come to the conclusion that four to five categories of astrophysical events must have contributed. These include the ejection of Fe and trans-Fe elements Sr, Y, Zr (continuing possibly beyond to slightly higher mass numbers) in category 0 events (hereafter "C0"), Fe and weak r-process contributions (including Eu in moderate to slightly larger but varying amounts) in CI and CII events, strong r-process abundance patterns with no or negligible (in comparison to solar) Fe production in CIIIa and CIIIb events, where category CIIIb shows a tendency for an actinide boost behavior. When comparing these categories with presently existing nucleosynthesis predictions, we suggest to identify them (despite remaining uncertainties) with regular core-collapse supernovae, quark deconfinement supernovae, magneto-rotational supernovae, neutron star mergers, and outflows from black hole accretion tori.