111 research outputs found
Composition Effects on Kilonova Spectra and Light Curves: I
The merger of neutron star binaries is believed to eject a wide range of
heavy elements into the universe. By observing the emission from this ejecta,
scientists can probe the ejecta properties (mass, velocity and composition
distributions). The emission (a.k.a. kilonova) is powered by the radioactive
decay of the heavy isotopes produced in the merger and this emission is
reprocessed by atomic opacities to optical and infra-red wavelengths.
Understanding the ejecta properties requires calculating the dependence of this
emission on these opacities. The strong lines in the optical and infra-red in
lanthanide opacities have been shown to significantly alter the light-curves
and spectra in these wavelength bands, arguing that the emission in these
wavelengths can probe the composition of this ejecta. Here we study variations
in the kilonova emission by varying individual lanthanide (and the actinide
uranium) concentrations in the ejecta. The broad forest of lanthanide lines
makes it difficult to determine the exact fraction of individual lanthanides.
Nd is an exception. Its opacities above 1 micron are higher than other
lanthanides and observations of kilonovae can potentially probe increased
abundances of Nd. Similarly, at early times when the ejecta is still hot (first
day), the U opacity is strong in the 0.2-1 micron wavelength range and kilonova
observations may also be able to constrain these abundances
Precision mass measurements on neutron-rich rare-earth isotopes at JYFLTRAP - reduced neutron pairing and implications for the -process calculations
The rare-earth peak in the -process abundance pattern depends sensitively
on both the astrophysical conditions and subtle changes in nuclear structure in
the region. This work takes an important step elucidating the nuclear structure
and reducing the uncertainties in -process calculations via precise atomic
mass measurements at the JYFLTRAP double Penning trap. Nd, Pm,
Sm, and Gd have been measured for the first time and the
precisions for Nd, Pm, Eu, Gd, and
Tb have been improved considerably. Nuclear structure has been probed
via two-neutron separation energies and neutron pairing energy metrics
. The data do not support the existence of a subshell closure at .
Neutron pairing has been found to be weaker than predicted by theoretical mass
models. The impact on the calculated -process abundances has been studied.
Substantial changes resulting in a smoother abundance distribution and a better
agreement with the solar -process abundances are observed.Comment: 8 pages, 4 figures, accepted for publication in Physical Review
Letter
Constraining inputs to realistic kilonova simulations through comparison to observed -process abundances
Kilonovae, one source of electromagnetic emission associated with neutron
star mergers, are powered by the decay of radioactive isotopes in the
neutron-rich merger ejecta. Models for kilonova emission consistent with the
electromagnetic counterpart to GW170817 predict characteristic abundance
patterns, determined by the relative balance of different types of material in
the outflow. Assuming the observed source is prototypical, this inferred
abundance pattern in turn must match -process abundances deduced by other
means, such as what is observed in the solar system. We report on analysis
comparing the input mass-weighted elemental compositions adopted in our
radiative transfer simulations to the mass fractions of elements in the Sun, as
a practical prototype for the potentially universal abundance signature from
neutron-star mergers. We characterize the extent to which our parameter
inference results depend on our assumed composition for the dynamical and wind
ejecta and examine how the new results compare to previous work. We find that a
dynamical ejecta composition calculated using the FRDM2012 nuclear mass and
FRLDM fission models with extremely neutron-rich ejecta ()
along with moderately neutron-rich () wind ejecta composition
yields a wind-to-dynamical mass ratio of = 0.47 which
best matches the observed AT2017gfo kilonova light curves while also producing
the best-matching abundance of neutron-capture elements in the solar system.Comment: 16 pages, 9 figures, submitted to PR
Executive Summary of the Topical Program: Nuclear Isomers in the Era of FRIB
We report on the Facility for Rare Isotope Beams (FRIB) Theory Alliance
topical program "Nuclear Isomers in the Era of FRIB". We outline the many ways
isomers influence and contribute to nuclear science and technology, especially
in the four FRIB pillars: properties of rare isotopes, nuclear astrophysics,
fundamental symmetries, and applications for the nation and society. We
conclude with a resolution stating our recommendation that the nuclear physics
community actively pursue isomer research. A white paper is forthcoming.Comment: 4 pages including reference
Ă-delayed neutron emission of r-process nuclei at the N=82 shell closure
Theoretical models of Ă-delayed neutron emission are used as crucial inputs in r-process calculations. Benchmarking the predictions of these models is a challenge due to a lack of currently available experimental data. In this work the Ă-delayed neutron emission probabilities of 33 nuclides in the important mass regions south and south-west of 132Sn are presented, 16 for the first time. The measurements were performed at RIKEN using the Advanced Implantation Detector Array (AIDA) and the BRIKEN neutron detector array. The values presented constrain the predictions of theoretical models in the region, affecting the final abundance distribution of the second r-process peak at .Peer ReviewedArticle signat per 58 autors/es
J. Liu, S. Bae, N.T. Brewer, C.G. Bruno, R. Caballero-Folch, P.J. Coleman-Smith, I. Dillmann, C. Domingo-Pardo, A. Fijalkowska, N. Fukuda, S. Go, C.J. Griffin, R. Grzywacz, J. Ha, L. J. Harkness-Brennan, T. Isobe, D. Kahl, L.H. Khiem, G.G. Kiss, A. Korgul, S. Kubono, M. Labiche, I. Lazarus, P. Morrall, M.R. Mumpower, N. Nepal, R.D. Page, M. Piersa , V.F.E. Pucknell , B.C. Rasco, B. Rubio, K.P. Rykaczewski , H. Sakurai , Y. Shimizu , D.W. Stracener, T. Sumikama , H. Suzuki, J.L. Tain , H. Takeda, A. Tarifeño-Saldivia, A. Tolosa-Delgado , M. Wolinska-Cichocka , R. YokoyamaPostprint (author's final draft
Catching Element Formation In The Act
Gamma-ray astronomy explores the most energetic photons in nature to address
some of the most pressing puzzles in contemporary astrophysics. It encompasses
a wide range of objects and phenomena: stars, supernovae, novae, neutron stars,
stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays
and relativistic-particle acceleration, and the evolution of galaxies. MeV
gamma-rays provide a unique probe of nuclear processes in astronomy, directly
measuring radioactive decay, nuclear de-excitation, and positron annihilation.
The substantial information carried by gamma-ray photons allows us to see
deeper into these objects, the bulk of the power is often emitted at gamma-ray
energies, and radioactivity provides a natural physical clock that adds unique
information. New science will be driven by time-domain population studies at
gamma-ray energies. This science is enabled by next-generation gamma-ray
instruments with one to two orders of magnitude better sensitivity, larger sky
coverage, and faster cadence than all previous gamma-ray instruments. This
transformative capability permits: (a) the accurate identification of the
gamma-ray emitting objects and correlations with observations taken at other
wavelengths and with other messengers; (b) construction of new gamma-ray maps
of the Milky Way and other nearby galaxies where extended regions are
distinguished from point sources; and (c) considerable serendipitous science of
scarce events -- nearby neutron star mergers, for example. Advances in
technology push the performance of new gamma-ray instruments to address a wide
set of astrophysical questions.Comment: 14 pages including 3 figure
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