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![-Observational data of metal-poor stars and EMPs showing the scatter in [Sr/Ba] as a function of metallicity (Suda et al. 2008). Stars that are potentially contaminated by the s-process, as discussed in Aoki et al. (2013); CS 30322-023, CS 29493-090, HE 0305-4520, CS 22946-011, CS 22941-005, and CS 22950-173 are indicated by filled circles.](profile/Michael-Famiano-2/publication/303969763/figure/fig3/AS:667842554904596@1536237481742/Observational-data-of-metal-poor-stars-and-EMPs-showing-the-scatter-in-Sr-Ba-as-a.png)
-Observational data of metal-poor stars and EMPs showing the scatter in [Sr/Ba] as a function of metallicity (Suda et al. 2008). Stars that are potentially contaminated by the s-process, as discussed in Aoki et al. (2013); CS 30322-023, CS 29493-090, HE 0305-4520, CS 22946-011, CS 22941-005, and CS 22950-173 are indicated by filled circles.
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![Fig. 6.— GCE results for [Sr/Fe], [Ba/Fe], and [Eu/Fe] as a function of...](profile/Michael-Famiano-2/publication/303969763/figure/fig1/AS:373151490953218@1465977656330/GCE-results-for-Sr-Fe-Ba-Fe-and-Eu-Fe-as-a-function-of-metallicity-assuming-a_Q320.jpg)
![Fig. 7.-Results of the GCE calculation showing [Sr/Ba] as a function of...](profile/Michael-Famiano-2/publication/303969763/figure/fig6/AS:667842554888216@1536237481820/Results-of-the-GCE-calculation-showing-Sr-Ba-as-a-function-of-metallicity-halo-stars_Q320.jpg)
A model is proposed in which the light r-process element enrichment in metal-poor stars is explained via enrichment from a truncated r-process, or "tr-process." The truncation of the r-process from a generic core-collapse event followed by a collapse into an accretion-induced black hole is examined in the framework of a galactic chemical evolution...
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... While the Shen EoS is based on a relativistic mean field model [49][50][51], the LS220 EoS is based on a Skyrme energy-density functional [52]. These EoSs have been widely used to simulate various astrophysical phenomena [53][54][55][56][57][58][59][60]. The Togashi EoS [61] is constructed with use of a realistic two-body potential and a phenomenological three-body potential [62][63][64] under a finite temperature. ...
... In our cooling calculations as described in the previous section, the neutron star surface is assumed to have light compositions, i.e., 73% 1 H, 25% 4 He, and 2% 56 Ni. Many previous studies show that the surface compositions affect the effective surface temperature of INS [33,34]. ...
Whether fast cooling processes occur or not is crucial for the thermal evolution of neutron stars. In particular, the threshold of the direct Urca process, which is one of the fast cooling processes, is determined by the interior proton fraction $Y_p$, or the nuclear symmetry energy. Since recent observations indicate the small radius of neutron stars, a low value is preferred for the symmetry energy. In this study, simulations of neutron star cooling are performed adopting three models for the equation of state (EoS): Togashi, Shen, and LS220 EoSs. The Togashi EoS has been recently constructed with realistic nuclear potentials under finite temperature, and found to account for the small radius of neutron stars. As a result, we find that, since the direct Urca process is forbidden, the neutron star cooling is slow with use of the Togashi EoS. This is because the symmetry energy of Togashi EoS is lower than those of other EoSs. Hence, in order to account for observed age and surface temperature of isolated neutron stars with the use of the Togashi EoS, other fast cooling processes are needed regardless of the surface composition.
... The abundance patterns for some observed stars do not fit the standard r-process. In [502,503] it was hypothesized that such abundance patterns might be produced by failed supernovae. In particular they considered stars for which their core at first collapses to form a neutron star. ...
... This conclusion, however, is very dependent upon nuclear properties of the light neutron-rich nuclei along the r-process path and requires a much more detailed simulation of the relevant astrophysics. In Famiano et al. [503] it was shown that the scatter of [Sr/Ba] in metal-poor stars is very sensitive to the adopted equation of state, and hence, might be used as a diagnostic. ...
The rapid neutron capture process (r process) is believed to be responsible for about half of the production of the elements heavier than iron and contributes to abundances of some lighter nuclides as well. A universal pattern of r-process element abundances is observed in some metal-poor stars of the Galactic halo. This suggests that a well-regulated combination of astrophysical conditions and nuclear physics conspires to produce such a universal abundance pattern. The search for the astrophysical site for r-process nucleosynthesis has stimulated interdisciplinary research for more than six decades. There is currently much enthusiasm surrounding evidence for r-process nucleosynthesis in binary neutron star mergers in the multi-wavelength follow-up observations of kilonova/gravitational-wave GRB170807A/GW170817. Nevertheless, there remain questions as to the contribution over the history of the Galaxy to the current solar-system r-process abundances from other sites such as neutrino-driven winds or magnetohydrodynamical ejection of material from core-collapse supernovae. In this review we highlight some current issues surrounding the nuclear physics input, astronomical observations, galactic chemical evolution, and theoretical simulations of r-process astrophysical environments with the goal of outlining a path toward resolving the remaining mysteries of the r process.
In the early Galaxy, elemental abundances of the extremely metal-poor (EMP) stars contain abundant information about the neutron-capture nucleosynthesis and the chemical enrichment history. In this work, we study the abundance characteristics of Sr and Ba for the EMP stars in the [Sr/Ba] vs. [Ba/Fe] space. We find that there are three boundaries for the distribution region of the EMP stars. The weak r-process star CS 22897–008 lies on the upper end and the main r-process stars lie on the right end of the region. Near the right boundary of the distribution region, there is an Fe-normal belt. For the EMP stars in the belt, element Fe dominantly originates from the normal massive stars. The low-Sr stars ([Sr/Fe]≤−0.3) distribute in the region of the lower left of the Fe-normal belt and their Fe should originate partly from the prompt inventory. We find that the formation of the lower boundary of the distribution region is due to the pollution of the main r-process material and the formation of the right boundary could be explained by the combination of the weak r- and main r-process material. Furthermore, the formation of the left boundary is due to the pollution of the weak r-process material. Although the [Sr/Ba] ratios are related to the relative importance of the weak r-process material, the scatter of [Sr/Ba] ratios for the EMP stars mainly depends on the abundance ratio of the weak r-process.
The rapid neutron capture process (r process)is believed to be responsible for about half of the production of the elements heavier than iron and contributes to abundances of some lighter nuclides as well. A universal pattern of r-process element abundances is observed in some metal-poor stars of the Galactic halo. This suggests that a well-regulated combination of astrophysical conditions and nuclear physics conspires to produce such a universal abundance pattern. The search for the astrophysical site for r-process nucleosynthesis has stimulated interdisciplinary research for more than six decades. There is currently much enthusiasm surrounding evidence for r-process nucleosynthesis in binary neutron star mergers in the multi-wavelength follow-up observations of kilonova/gravitational-wave GRB170807A/GW170817. Nevertheless, there remain questions as to the contribution over the history of the Galaxy to the current solar-system r-process abundances from other sites such as neutrino-driven winds or magnetohydrodynamical ejection of material from core-collapse supernovae. In this review we highlight some current issues surrounding the nuclear physics input, astronomical observations, galactic chemical evolution, and theoretical simulations of r-process astrophysical environments with the goal of outlining a path toward resolving the remaining mysteries of the r process.
