Almudena Arcones

MAGNETOROTATIONALLY DRIVEN SUPERNOVAE AS THE ORIGIN OF EARLY GALAXY r-PROCESS ELEMENTS?

We examine magnetorotationally driven supernovae as sources of r-process elements in the early Galaxy. On the basis of thermodynamic histories of tracer particles from a three-dimensional magnetohydrodynamical core-collapse supernova model with approximated neutrino transport, we perform nucleosynthesis calculations with and without considering the effects of neutrino absorption reactions on the electron fraction (Ye ) during post-processing. We find that the peak distribution of Ye in the ejecta is shifted from ~0.15 to ~0.17 and broadened toward higher Ye due to neutrino absorption. Nevertheless, in both cases, the second and third peaks of the solar r-process element distribution can be reproduced well. The rare progenitor configuration that was used here, characterized by a high rotation rate and a large magnetic field necessary for the formation of bipolar jets, could naturally provide a site for the strong r-process in agreement with observations of the early Galactic chemical evolution.

Europium production : neutron star mergers versus core-collapse supernovae

We have explored the Eu production in the Milky Way by means of a very detailed chemical evolution model. In particular, we have assumed that Eu is formed in merging neutron star (or neutron star black hole) binaries as well as in type II sup ernovae. We have tested the effects of several important parameters influencing the pro duction of Eu during the merging of two neutron stars, such as: i) the time scale of coalescenc e, ii) the Eu yields and iii) the range of initial masses for the progenitors of the neutron st ars. The yields of Eu from type II supernovae are very uncertain, more than those from coalescing neutron stars, so we have explored several possibilities. We have compared our model results with the observed rate of coalescence of neutron stars, the solar Eu abundance, the [Eu/Fe] versus [Fe/H] relation in the solar vicinity and the [Eu/H] gradient along the Galactic disc. Our main results can be summarized as follows: i) neutron star mergers can be entirely responsible for the production of Eu in the Galaxy if the coalescence time scale is no longer than 1 Myr for the bulk of binary systems, the Eu yield is around 3 × 10 −7 M⊙, and the mass range of progenitors of neutron stars is 9‐50 M⊙; ii) both type II supernovae and merging neutron stars can produce the right amount of Eu if the neutron star mergers produce 2 × 10 −7 M⊙ per system and type II supernovae, with progenitors in the range 20‐50 M⊙, produce yields of Eu of the order of 10 −8 ‐10 −9 M⊙; iii) either models with only neutron stars producing Eu or mixed ones can reproduce the observed Eu abundance gradient along the Galactic disc.

Neutrino-driven wind simulations and nucleosynthesis of heavy elements

Neutrino-driven winds, which follow core-collapse supernova explosions, present a fascinating nuclear-astrophysics problem that requires an understanding of advanced astrophysics simulations, the properties of matter and neutrino interactions under extreme conditions, the structure and reactions of exotic nuclei, and comparisons with forefront astronomical observations. The neutrino-driven wind has attracted vast attention over the last 20 years as it was suggested as a candidate for the astrophysics site where half of the heavy elements are produced via the r-process. In this review, we summarize our present understanding of neutrino-driven winds from the dynamical and nucleosynthesis perspectives. Rapid progress has been made during recent years in understanding the wind with improved simulations and better micro physics. The current status of the fields is that hydrodynamical simulations do not reach the extreme conditions necessary for the r-process, and the proton or neutron richness of the wind remains to be investigated in more detail. However, nucleosynthesis studies and observations already point to neutrino-driven winds to explain the origin of lighter heavy elements, such as Sr, Y, Zr.

NEUTRINO-DRIVEN WINDS IN THE AFTERMATH OF A NEUTRON STAR MERGER: NUCLEOSYNTHESIS AND ELECTROMAGNETIC TRANSIENTS

We present a comprehensive nucleosynthesis study of the neutrino-driven wind in the aftermath of a binary neutron star merger. Our focus is the initial remnant phase when a massive central neutron star is present. Using tracers from a recent hydrodynamical simulation, we determine total masses and integrated abundances to characterize the composition of unbound matter. We find that the nucleosynthetic yields depend sensitively on both the life time of the massive neutron star and the polar angle. Matter in excess of up to

The effects of r-process heating on fallback accretion in compact object mergers

9 \cdot 10^{-3} M_\odot

LTE or non-LTE, that is the question - The NLTE chemical evolution of strontium in extremely metal-poor stars

becomes unbound until

THE ROLE OF FISSION IN NEUTRON STAR MERGERS AND ITS IMPACT ON THE r-PROCESS PEAKS

\sim 200~{\rm ms}

HOW MANY NUCLEOSYNTHESIS PROCESSES EXIST AT LOW METALLICITY

. Due to electron fractions of

High-resolution simulations of the head-on collision of white dwarfs

Y_{\rm e} \approx 0.2 - 0.4

r -process nucleosynthesis from matter ejected in binary neutron star mergers

mainly nuclei with mass numbers