arXiv subjects

M. Jacobi

Publications and source records attributed to M. Jacobi.

4 recordsLinked to original sources

arXiv2023

Neutrino-Driven Outflows and the Elemental Abundance Patterns of Very Metal-Poor Stars

The elemental abundances between strontium and silver ($Z = 38-47$) observed in the atmospheres of very metal-poor stars (VMP) in the Galaxy may contain the fingerprint of the weak $r$-process and $\nu p$-process occurring in early core-collapse supernovae explosions. In this work, we combine various astrophysical conditions based on a steady-state model to cover the richness of the supernova ejecta in terms of entropy, expansion timescale, and electron fraction. The calculated abundances based on different combinations of conditions are compared with stellar observations with the aim of constraining supernova ejecta conditions. We find that some conditions of the neutrino-driven outflows consistently reproduce the observed abundances of our sample. In addition, from the successful combinations, the neutron-rich trajectories better reproduce the observed abundances of Sr-Zr ($Z= 38-40$), while the proton-rich ones, Mo-Pd ($Z= 42-47$).

astro-ph.HE↗

arXiv2023

The nuclear reaction network WinNet

We present the state-of-the-art single-zone nuclear reaction network WinNet that is capable of calculating the nucleosynthetic yields of a large variety of astrophysical environments and conditions. This ranges from the calculation of the primordial nucleosynthesis, where only a few nuclei are considered, to the ejecta of neutron star mergers with several thousands of involved nuclei. Here we describe the underlying physics and implementation details of the reaction network. We additionally present the numerical implementation of two different integration methods, the implicit Euler method and Gears method along with their advantages and disadvantages. We furthermore describe basic example cases of thermodynamic conditions that we provide together with the network and demonstrate the reliability of the code by using simple test cases. With this publication, WinNet is publicly available and open source at GitHub and Zenodo.

astro-ph.IM↗

arXiv2022

Constraining nucleosynthesis in neutrino-driven winds: observations, simulations and nuclear physics

A promising astrophysical site to produce the lighter heavy elements of the first $r$-process peak ($Z = 38-47$) is the moderately neutron rich ($0.4 < Y_e < 0.5$) neutrino-driven ejecta of explosive environments, such as core-collapse supernovae and neutron star mergers, where the weak $r$-process operates. This nucleosynthesis exhibits uncertainties from the absence of experimental data from $(\alpha,xn)$ reactions on neutron-rich nuclei, which are currently based on statistical model estimates. In this work, we report on a new study of the nuclear reaction impact using a Monte Carlo approach and improved $(\alpha,xn)$ rates based on the Atomki-V2 $\alpha$ Optical Model Potential ($\alpha$OMP). We compare our results with observations from an up-to-date list of metal-poor stars with [Fe/H] $<$ -1.5 to find conditions of the neutrino-driven wind where the lighter heavy elements can be synthesized. We identified a list of $(\alpha,xn)$ reaction rates that affect key elemental ratios in different astrophysical conditions. Our study aims on motivating more nuclear physics experiments on $(\alpha, xn)$ reactions using current and the new generation of radioactive beam facilities and also more observational studies of metal-poor stars.

astro-ph.HE↗

arXiv2020

Low Energy measurement of the $^{96}\mathrm{Zr}(\alpha,n)^{99}\mathrm{Mo}$ reaction cross section and its impact on weak r-process nucleosynthesis

Lighter heavy elements beyond iron and up to around silver can form in neutrino-driven ejecta in core-collapse supernovae and neutron star mergers. Slightly neutron-rich conditions favour a weak r-process that follows a path close to stability. Therefore, the beta decays are slow compared to the expansion time scales, and ($\alpha$,n) reactions become critical to move matter towards heavier nuclei. The rates of these reactions are calculated with the statistical model and their main uncertainty, at energies relevant for the weak r-process, is the $\alpha$+nucleus optical potential. There are several sets of parameters to calculate the $\alpha$+nucleus optical potential leading to large deviations for the reaction rates, exceeding even one order of magnitude. Recently the $^{96}$Zr($\alpha$,n)$^{99}$Mo reaction has been identified as a key reaction that impacts the production of elements from Ru to Cd. Here, we present the first cross section measurement of this reaction at energies (6.22 MeV $\leq$ E$_\mathrm{c.m.}$ $\leq$ 12.47 MeV) relevant for the weak r-process. The new data provide a stringent test of various model predictions which is necessary to improve the precision of the weak r-process network calculations. The strongly reduced reaction rate uncertainty leads to very well-constrained nucleosynthesis yields for $Z = 44 - 48$ isotopes under different neutrino-driven wind conditions.

nucl-ex↗