scholarly journals Probing the fission properties of neutron-rich actinides with the astrophysical r process

2020 ◽  
Vol 242 ◽  
pp. 04002
Author(s):  
Nicole Vassh ◽  
Matthew Mumpower ◽  
Trevor Sprouse ◽  
Rebecca Surman ◽  
Ramona Vogt
Keyword(s):  
Recent Work ◽  
Fission Fragment ◽  
Neutron Capture ◽  
Fission Barriers ◽  
R Process ◽  
Process Elements ◽  
The Impact ◽  
Heavy Actinide

We review recent work examining the influence of fission in rapid neutron capture (r-process) nucleosynthesis which can take place in astrophysical environments. We briefly discuss the impact of uncertain fission barriers and fission rates on the population of heavy actinide species. We demonstrate the influence of the fission fragment distributions for neutron-rich nuclei and discuss currently available treatments, including recent macroscopic-microscopic calculations. We conclude by comparing our nucleosynthesis results directly with stellar data for metal-poor stars rich in r-process elements to consider whether fission plays a role in the so-called ‘universality’ of r-process abundances observed from star to star.

scholarly journals Constraining nucleosynthesis in two CEMP progenitors using fluorine

2020 ◽  
Vol 498 (3) ◽  
pp. 3549-3559
Author(s):  
Aldo Mura-Guzmán ◽  
D Yong ◽  
C Abate ◽  
A Karakas ◽  
C Kobayashi ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Slow Neutron ◽  
Asymptotic Giant Branch ◽  
Capture Process ◽  
Upper Limit ◽  
Infrared Spectrometer ◽  
Binary Evolution ◽  
Vibration Rotation ◽  
R Process ◽  
Process Elements

ABSTRACT We present new fluorine abundance estimations in two carbon enhanced metal-poor (CEMP) stars, HE 1429−0551 and HE 1305+0007. HE 1429−0551 is also enriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE 1305+0007 is enhanced in both, slow and rapid neutron-capture process elements, a CEMP-s/r. The F abundances estimates are derived from the vibration–rotation transition of the HF molecule at 23358.6 Å  using high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) at the 4-m class Lowell Discovery Telescope. Our results include an F abundance measurement in HE 1429−0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = −2.53, and an F upper limit in HE 1305+0007 of A(F) < +3.28 ([F/Fe] < +1.00) at [Fe/H] = −2.28. Our new derived F abundance in HE 1429−0551 makes this object the most metal-poor star where F has been detected. We carefully compare these results with literature values and state-of-the-art CEMP-s model predictions including detailed asymptotic giant branch (AGB) nucleosynthesis and binary evolution. The modelled fluorine abundance for HE 1429−0551 is within reasonable agreement with our observed abundance, although is slightly higher than our observed value. For HE 1429−0551, our findings support the scenario via mass transfer by a primary companion during its thermally pulsing phase. Our estimated upper limit in HE 1305+0007, along with data from the literature, shows large discrepancies compared with AGB models. The discrepancy is principally due to the simultaneous s- and r-process element enhancements which the model struggles to reproduce.

scholarly journals Unusual neutron-capture nucleosynthesis in a carbon-rich Galactic bulge star

2019 ◽  
Vol 622 ◽  
pp. A159 ◽  
Author(s):  
Andreas Koch ◽  
Moritz Reichert ◽  
Camilla Juul Hansen ◽  
Melanie Hampel ◽  
Richard J. Stancliffe ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Galactic Halo ◽  
Asymptotic Giant Branch ◽  
Galactic Bulge ◽  
Element Abundances ◽  
Intermediate Neutron ◽  
Low Mass ◽  
Process Component ◽  
Process Elements ◽  
The Impact

Metal-poor stars in the Galactic halo often show strong enhancements in carbon and/or neutron-capture elements. However, the Galactic bulge is notable for its paucity of these carbon-enhanced metal-poor (CEMP) and/or CH-stars, with only two such objects known to date. This begs the question whether the processes that produced their abundance distribution were governed by a comparable nucleosynthesis in similar stellar sites as for their more numerous counterparts in the halo. Recently, two contenders of these classes of stars were discovered in the bulge, at [Fe/H] = −1.5 and −2.5 dex, both of which show enhancements in [C/Fe] of 0.4 and 1.4 dex (respectively), [Ba/Fe] in excess of 1.3 dex, and also elevated nitrogen. The more metal-poor of the stars can be well matched by standard s-process nucleosynthesis in low-mass asymptotic giant branch (AGB) polluters. The other star shows an abnormally high [Rb/Fe] ratio. Here, we further investigate the origin of the abundance peculiarities in the Rb-rich star by new, detailed measurements of heavy element abundances and by comparing the chemical element ratios of 36 species to several models of neutron-capture nucleosynthesis. The i-process with intermediate neutron densities between those of the slow (s-) and rapid (r)-neutron-capture processes has been previously found to provide good matches of CEMP stars with enhancements in both r- and s-process elements (class CEMP-r/s), rather than invoking a superposition of yields from the respective individual processes. However, the peculiar bulge star is incompatible with a pure i-process from a single ingestion event. Instead, it can, statistically, be better reproduced by more convoluted models accounting for two proton ingestion events, or by an i-process component in combination with s-process nucleosynthesis in low-to-intermediate mass (2–3 M⊙) AGB stars, indicating multiple polluters. Finally, we discuss the impact of mixing during stellar evolution on the observed abundance peculiarities.

scholarly journals Carbon-Enhanced Metal-Poor (CEMP) stars

2009 ◽  
Vol 5 (S265) ◽  
pp. 111-116 ◽  
Author(s):  
Wako Aoki
Keyword(s):  
Neutron Capture ◽  
Significant Fraction ◽  
Agb Stars ◽  
Iron Deficient ◽  
R Process ◽  
Process Elements

AbstractA significant fraction of metal-poor stars have large over-abundances of carbon, and are called Carbon-Enhanced Metal-Poor (CEMP) stars. Most of CEMP stars also show excesses of heavy neutron-capture elements like Ba, indicating that their origin is the nucleosynthesis in AGB stars. Remaining CEMP stars that have Ba abundances as low as non-carbon-rich stars appear in the lowest metallicity range ([Fe/H]≲−2.5), and connections with the two most iron-deficient stars (so-called Hyper Metal-Poor stars) are suggested. Although the origins of the carbon-excesses in these objects have not been well identified, some objects suggest contributions of faint supernovae. Remaining problems on CEMP stars, such as the binary fraction, excess of r-process elements, are discussed.

Mechanisms for the Reactions Following Radiative Neutron Capture in Liquid Organic Halides

1962 ◽  
Vol 1 (1) ◽  
Author(s):  
Miriam Milman
Keyword(s):  
Recent Work ◽  
Neutron Capture ◽  
Impact Model ◽  
Unified Approach ◽  
Halogen Atoms ◽  
Organic Halides ◽  
Radiative Neutron ◽  
Radiative Neutron Capture ◽  
Work Done ◽  
The Impact

SummaryThe available data together with some recent work done by the author, have been reconsidered with regard to establishing a unified approach to the chemistry of hot atoms. It was found that the "Impact Model", originally proposed for the hot reactions of tritium atoms in gases, can also give an adequate picture for the reactions of activated halogen atoms in liquid organic halides.

scholarly journals r-Process Elements as Tracers of Enrichment Processes in the Early Halo

2015 ◽  
Vol 11 (S317) ◽  
pp. 272-273
Author(s):  
Johannes Andersen ◽  
Birgitta Nordström ◽  
Terese T. Hansen
Keyword(s):  
Mass Transfer ◽  
Neutron Capture ◽  
Binary Systems ◽  
Chemical Enrichment ◽  
Halo Stars ◽  
Standard Scenario ◽  
R Process ◽  
Process Elements

AbstractSignificant minorities of extremely metal-poor (EMP) halo stars exhibit dramatic excesses of neutron capture elements. The standard scenario for their origin is mass transfer and dilution in binary systems, but requires them to be binaries. If not, these excesses must have been implanted in them from birth by processes that are not included in current models of SN II chemical enrichment. The binary population of such EMP subgroups is a test of this scenario.

scholarly journals 129I and 247Cm in meteorites constrain the last astrophysical source of solar r-process elements

Science ◽  
2021 ◽  
Vol 371 (6532) ◽  
pp. 945-948 ◽  
Author(s):  
Benoit Côté ◽  
Marius Eichler ◽  
Andrés Yagüe López ◽  
Nicole Vassh ◽  
Matthew R. Mumpower ◽  
...  
Keyword(s):  
Neutron Star ◽  
Solar System ◽  
Neutron Capture ◽  
Nuclear Physics ◽  
Early Solar System ◽  
Capture Process ◽  
Astrophysical Source ◽  
R Process ◽  
Process Elements

The composition of the early Solar System can be inferred from meteorites. Many elements heavier than iron were formed by the rapid neutron capture process (r-process), but the astrophysical sources where this occurred remain poorly understood. We demonstrate that the near-identical half-lives (≃15.6 million years) of the radioactive r-process nuclei iodine-129 and curium-247 preserve their ratio, irrespective of the time between production and incorporation into the Solar System. We constrain the last r-process source by comparing the measured meteoritic ratio 129I/247Cm = 438 ± 184 with nucleosynthesis calculations based on neutron star merger and magneto-rotational supernova simulations. Moderately neutron-rich conditions, often found in merger disk ejecta simulations, are most consistent with the meteoritic value. Uncertain nuclear physics data limit our confidence in this conclusion.

scholarly journals Chemical evolution of r-process elements in the Draco dwarf spheroidal galaxy

2015 ◽  
Vol 11 (S317) ◽  
pp. 310-311
Author(s):  
M. N. Ishigaki ◽  
T. Tsujimoto ◽  
T. Shigeyama ◽  
W. Aoki
Keyword(s):  
Neutron Star ◽  
High Resolution ◽  
Neutron Capture ◽  
Milky Way ◽  
Origin And Evolution ◽  
Dwarf Spheroidal Galaxies ◽  
Giant Stars ◽  
Upper Limits ◽  
R Process ◽  
Process Elements

AbstractA dominant astrophysical site for r-process, which is responsible for producing heavy neutron-capture elements, is unknown. Dwarf spheroidal galaxies around the Milky Way halo provide ideal laboratories to investigate the origin and evolution of r-process elements. We carried out high-resolution spectroscopic observations of three giant stars in the Draco dwarf spheroidal galaxy to estimate their europium abundances. We found that the upper-limits of [Eu/H] are very low in the range [Fe/H] < −2, while this ratio is nearly constant at higher metallicities. This trend is not well reproduced with models which assume that Eu is produced together with Fe by SNe, and may suggest the contribution from other objects such as neutron-star mergers.

scholarly journals Silver Stars

2009 ◽  
Vol 5 (S265) ◽  
pp. 67-68
Author(s):  
Camilla Juul Hansen ◽  
Francesca Primas
Keyword(s):  
Neutron Capture ◽  
Heavy Elements ◽  
Capture Process ◽  
Elemental Abundances ◽  
The Galaxy ◽  
Formation And Evolution ◽  
R Process ◽  
Process Elements ◽  
Heaviest Elements ◽  
Process Element

AbstractThe rapid neutron-capture process (r-process), which produces some of the heaviest elements, is not well understood. Obtaining accurate abundances of these heavy elements (Z > 38) is important, both in the context of the chemical evolution of the Galaxy and for understanding the site(s) and process(es) of formation of those elements. We have determined elemental abundances for several r-process elements, notably silver, from high resolution VLT/UVES spectra. Silver was chosen because it is predominantly a light r-process element (38 < Z < 50), and little is known about its formation and evolution in the Galaxy. Here, we present our preliminary results.

Distribution of R- and S-Process Elements in the Galactic Halo

1988 ◽  
Vol 132 ◽  
pp. 501-506
Author(s):  
C. Sneden ◽  
C. A. Pilachowski ◽  
K. K. Gilroy ◽  
J. J. Cowan
Keyword(s):  
Heavy Element ◽  
Galactic Halo ◽  
Low Noise ◽  
Heavy Elements ◽  
Process Synthesis ◽  
Element Abundances ◽  
Halo Stars ◽  
Abundance Patterns ◽  
R Process ◽  
Process Elements

Current observational results for the abundances of the very heavy elements (Z&gt;30) in Population II halo stars are reviewed. New high resolution, low noise spectra of many of these extremely metal-poor stars reveal general consistency in their overall abundance patterns. Below Galactic metallicities of [Fe/H] Ã −2, all of the very heavy elements were manufactured almost exclusively in r-process synthesis events. However, there is considerable star-to-star scatter in the overall level of very heavy element abundances, indicating the influence of local supernovas on element production in the very early, unmixed Galactic halo. The s-process appears to contribute substantially to stellar abundances only in stars more metal-rich than [Fe/H] Ã −2.

scholarly journals Fission fragment distributions and their impact on the r -process nucleosynthesis in neutron star mergers

2021 ◽  
Vol 103 (2) ◽  
Author(s):  
J.-F. Lemaître ◽  
S. Goriely ◽  
A. Bauswein ◽  
H.-T. Janka
Keyword(s):  
Neutron Star ◽  
Fission Fragment ◽  
R Process
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