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10 pages, 310 KB

Open AccessArticle

Constraining Neutron-Capture Nucleosynthesis from Surface Chemical Composition of Chemically Peculiar Stars: The Puzzling Case of HE 1005-1439

by Aruna Goswami, Arthur Choplin, Partha Pratim Goswami, Lionel Siess and Stephane Goriely

Galaxies 2026, 14(3), 37; https://doi.org/10.3390/galaxies14030037 - 23 Apr 2026

Abstract

The chemical composition of stellar atmospheres provides a valuable window into the complex processes of stellar nucleosynthesis. Among chemically peculiar cool stars, many objects are the products of mass transfer in binary systems, including most carbon stars, CH stars, and CEMP-s and [...] Read more.

The chemical composition of stellar atmospheres provides a valuable window into the complex processes of stellar nucleosynthesis. Among chemically peculiar cool stars, many objects are the products of mass transfer in binary systems, including most carbon stars, CH stars, and CEMP-s and CEMP-r/s stars. Accurate and precise determinations of heavy-element abundances in these systems serve as powerful tracers of neutron-capture nucleosynthesis operating in the slow (s) and intermediate (i) regimes. Such measurements also place important constraints on binary evolution, mass-transfer mechanisms, the onset of early s-process enrichment, and the astrophysical sites and production pathways associated with the i-process. In this work, we investigate the origin of the extremely metal-poor star HE 1005-1439, which has previously been suggested to exhibit a surface composition enriched by a combination of s- and i-process nucleosynthesis. Using new multi-zone, detailed AGB models for both the s- and i-processes, we find that a mixed

i + s

scenario provides a plausible explanation for the observed abundance pattern of HE 1005-1439, although a pure i-process AGB model yields an almost equally satisfactory fit. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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8 pages, 326 KB

Open AccessCommunication

Osmium Abundances in Galactic Halo Stars at Intermediate Metallicities

by Francesca Lucertini and Linda Lombardo

Galaxies 2026, 14(2), 31; https://doi.org/10.3390/galaxies14020031 - 9 Apr 2026

Viewed by 258

Abstract

Osmium is a third-peak neutron-capture element predominantly produced by the rapid (r-) process, and it is a valuable tracer of early Galactic chemical enrichment. However, osmium abundance measurements in Galactic stars remain limited due to observational challenges. We present new osmium abundances for [...] Read more.

Osmium is a third-peak neutron-capture element predominantly produced by the rapid (r-) process, and it is a valuable tracer of early Galactic chemical enrichment. However, osmium abundance measurements in Galactic stars remain limited due to observational challenges. We present new osmium abundances for 23 stars at intermediate metallicities (

- 2.5 \leq

[Fe/H]

\leq - 1.0

) within the framework of the MINCE (Measuring at Intermediate Metallicity Neutron-Capture Elements) project. A standard abundance analysis was carried out using one-dimensional LTE model atmospheres and the optical Os I line at 479 nm observed in high-quality UVES spectra. The derived [Os/Fe] ratio exhibits an anticorrelation with [Fe/H], supporting efficient r-process enrichment during the early phases of the Milky Way’s evolution. We also investigated Os abundances across different Galactic components, finding that halo and Gaia–Sausage–Enceladus stars are more Os-rich than thick-disk stars. A comparison between Os and europium abundances supports a common r-process origin for these elements at intermediate metallicities. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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8 pages, 1272 KB

Open AccessCommunication

First Results of the ⁶⁴Ni(n,γ) Cross Section Measurement at n_TOF

by Michele Spelta, Gabriele Cescutti, Sergio Cristallo, Francisco García-Infantes, Alice Manna, Alberto Mengoni, Paolo Maria Milazzo, Riccardo Mucciola, Giuseppe Tagliente, Diego Vescovi, Oliver Aberle, Victor Alcayne, Simone Amaducci, Józef Andrzejewski, Victor Babiano, Michael Bacak, Javier Balibrea-Correa, Ana-Paula Bernardes, Eric Berthoumieux, Roland Beyer, Marian Boromiza, Damir Bosnar, Manuel Caamaño, Francisco Calviño, Marco Calviani, Daniel Cano-Ott, Adrià Casanovas, Donato Castelluccio, Francesco Cerutti, Sotirios Chasapoglou, Enrico Chiaveri, Gerardo Claps, Paolo Colombetti, Nicola Colonna, Patrizio Console Camprini, Guillem Cortés, Miguel Cortés-Giraldo, Luigi Cosentino, Sophia Florence Dellmann, Maria Diakaki, Mario Di Castro, Mirco Dietz, César Domingo-Pardo, Rugard Dressler, Emmeric Dupont, Ignacio Durán, Zinovia Eleme, Mamad Eslami, Sylvain Fargier, Beatriz Fernández-Domínguez, Paolo Finocchiaro, Valter Furman, Aman Gandhi, Aleksandra Gawlik-Ramięga, Gianpiero Gervino, Simone Gilardoni, Enrique González-Romero, Styliani Goula, Erich Griesmayer, Carlos Guerrero, Frank Gunsing, Carlo Gustavino, Tanja Heftrich, Jan Heyse, William Hillman, David Jenkins, Erwin Jericha, Arnd Junghans, Yacine Kadi, Kalliopi Kaperoni, Michael Kokkoris, Dominik Koll, Yury Kopatch, Milan Krtička, Nikolaos Kyritsis, Ion Ladarescu, Claudia Lederer-Woods, Jorge Lerendegui-Marco, Giuseppe Lerner, Trinitario Martínez, Alessandro Masi, Cristian Massimi, Pierfrancesco Mastinu, Mario Mastromarco, Emilio-Andrea Maugeri, Annamaria Mazzone, Emilio Mendoza, Veatriki Michalopoulou, Elizabeth Musacchio González, Agatino Musumarra, Alexandru Negret, Nikolas Patronis, José Antonio Pavón, Maria Pellegriti, Pablo Pérez-Maroto, Alberto Pérez de Rada Fiol, Jarosław Perkowski, Cristina Petrone, Luciano Piersanti, Elisa Pirovano, Julio Plaza del Olmo, Dominik Plonka, Stephan Pomp, Ignacio Porras, Javier Praena, José-Manuel Quesada, René Reifarth, Dimitri Rochman, Yuriy Romanets, Annie Rooney, Carlo Rubbia, Adrián Sánchez-Caballero, Marta Sabaté-Gilarte, Daniele Scarpa, Peter Schillebeeckx, Dorothea Schumann, Gavin Smith, Nikolay Sosnin, Maria-Elisso Stamati, Antonella Tamburrino, Ariel Tarifeño-Saldivia, Diego Tarrío, Pablo Torres-Sánchez, Silvia Tosi, Giorgios Tsiledakis, Stanislav Valenta, Pedro Vaz, Gianfranco Vecchio, Vasilis Vlachoudis, Rosa Vlastou, Anton Wallner, Christina Weiss, Philip John Woods, Tobias Wright and Petar Žugec Show full author list Hide full author list

Galaxies 2026, 14(2), 29; https://doi.org/10.3390/galaxies14020029 - 8 Apr 2026

Viewed by 308

Abstract

The neutron capture cross section of ⁶⁴Ni is an important parameter in nuclear astrophysics that is needed to accurately simulate stellar nucleosynthesis and validate stellar models. ⁶⁴Ni is among the seeds of the s-process and its capture cross section has been [...] Read more.

The neutron capture cross section of ⁶⁴Ni is an important parameter in nuclear astrophysics that is needed to accurately simulate stellar nucleosynthesis and validate stellar models. ⁶⁴Ni is among the seeds of the s-process and its capture cross section has been found to have an important effect on the predicted abundances of many nuclei synthesized in Asymptotic Giant Branch (AGB) and massive stars. Despite its relevance, the measurements of the ⁶⁴Ni(n,

γ

) available in the literature are scarce and discrepant. For this reason, a new accurate time-of-flight measurement has been performed at the n_TOF facility at CERN, taking advantage of its high instantaneous neutron flux, and using a highly enriched ⁶⁴Ni sample. The first preliminary results show important discrepancies with respect to the cross sections recommended in the most recent releases of the evaluated nuclear data libraries. In particular, a large resonance reported at 9.52 keV is not observed. As a consequence, a significant reduction in the Maxwellian-Averaged Cross Section (MACS) obtained from evaluated data libraries in the 5–25 keV thermal energy region is expected. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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7 pages, 536 KB

Open AccessCommunication

Observations of r-Process Enriched Stars

by Terese T. Hansen, Mila Racca, Timothy C. Beers, Rana Ezzeddine, Anna Frebel, Erika M. Holmbeck, Vinicius M. Placco, Ian U. Roederer and Charli M. Sakari

Galaxies 2026, 14(2), 28; https://doi.org/10.3390/galaxies14020028 - 2 Apr 2026

Viewed by 364

Abstract

About half the elements heavier than iron in the universe, like silver and gold, are created in the rapid neutron-capture (r-)process. However, today, almost 70 years after the theoretical prediction of this process, it is still highly debated in what type [...] Read more.

About half the elements heavier than iron in the universe, like silver and gold, are created in the rapid neutron-capture (r-)process. However, today, almost 70 years after the theoretical prediction of this process, it is still highly debated in what type of stellar explosions it can take place. One of the best places to search for answers is in ancient, metal-poor stars formed from the enriched gas. Their chemical makeup is like a time capsule, a direct fingerprint of the elements produced by the stellar generations that came before them. Since the first highly r-process-enhanced star, CS 22892-052 was discovered more than 30 years ago, multiple projects like the Hamburg/ESO r-Process Enhanced Star (HERES) survey, the Chemical Evolution of r-process Elements in Stars (CERES) project, and the r-Process Alliance (RPA) have searched for more r-process-enriched stars in the Milky Way. At the same time, numerous r-process-enriched stars have been discovered in stellar streams and dwarf galaxies. Here we present an overview of recent advances in finding r-process-enriched metal-poor stars and what the detailed chemo-dynamical analysis of these stars can tell us about heavy element nucleosynthesis and the astrophysical site(s) of the r-process. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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7 pages, 420 KB

Open AccessCommunication

Molybdenum Abundances in MINCE Stars

by Linda Lombardo and Francesca Lucertini

Galaxies 2026, 14(2), 17; https://doi.org/10.3390/galaxies14020017 - 28 Feb 2026

Viewed by 615

Abstract

Molybdenum (Mo, Z = 42) is a neutron-capture element with seven stable isotopes that can be produced by different processes. Previous studies have shown a large scatter in molybdenum abundances for metal-poor ([Fe/H] <

- 1

) stars, indicating that multiple nucleosynthetic channels [...] Read more.

Molybdenum (Mo, Z = 42) is a neutron-capture element with seven stable isotopes that can be produced by different processes. Previous studies have shown a large scatter in molybdenum abundances for metal-poor ([Fe/H] <

- 1

) stars, indicating that multiple nucleosynthetic channels are responsible for molybdenum production even at very low metallicity. To understand which different nucleosynthesis processes are involved in the chemical enrichment of this element in the Galaxy, a large sample of precise molybdenum abundance is required. In this study, we present molybdenum abundances of 27 metal-poor stars from the Measuring at Intermediate Metallicity Neutron-Capture Elements project sample. We derived molybdenum abundances using three Mo i lines at 550.6 nm, 557.0 nm, and 603.0 nm, which proved to be reliable for measuring Mo abundances in giant stars with [Fe/H]

> - 2

. Our derived [Mo/Fe] abundance ratios show on average slightly higher values (∼0.2 dex) compared to the literature samples. This may be due to an observational bias or to non-local thermodynamic equilibrium effects. We also found that Gaia-Sausage-Enceladus candidate stars have lower [Mo/Fe] than the sample average, while the only Sequoia candidate star has a higher [Mo/Fe] than most sample stars. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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6 pages, 349 KB

Open AccessArticle

[Y/Mg] as a Stellar Chronometer: Combining Asteroseismic and Chemical Data

by Carlos Viscasillas Vázquez, Gražina Tautvaišienė, Erika Pakštienė, Arnas Drazdauskas, Yuriy Chorniy, Vilius Bagdonas, Šarūnas Mikolaitis, Renata Minkevičiūtė and Edita Stonkutė

Galaxies 2025, 13(6), 136; https://doi.org/10.3390/galaxies13060136 - 17 Dec 2025

Cited by 1 | Viewed by 885

Abstract

The determination of stellar ages remains one of the greatest challenges in astrophysics, as age cannot be directly measured. Advances over the last decade highlight a great potential of chemical clocks, particularly abundance ratios involving s-process and

α

-elements to estimate stellar [...] Read more.

The determination of stellar ages remains one of the greatest challenges in astrophysics, as age cannot be directly measured. Advances over the last decade highlight a great potential of chemical clocks, particularly abundance ratios involving s-process and

α

-elements to estimate stellar ages with improved precision. For a sample of 205 stars observed with the high-resolution spectrograph and 1.65 m telescope at the Molėtai Astronomical Observatory in Lithuania, we determined Y and Mg abundances and derived new asteroseismic ages from TESS observations. Our results reveal the dependence of the [Y/Mg]–age relationship on the Galactic birthplaces of thin-disc stars, while confirming previous results on negligible correlations for thick-disc stars. This study highlights the importance of integrating chemical compositions, asteroseismic data, and precise astrometric measurements from

G a i a

to refine the applicability of chemical clocks and enhance our understanding of Galactic chemical evolution. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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7 pages, 477 KB

Open AccessCommunication

Nucleosynthesis of Cobalt and Copper

by Beatriz Barbuy, Amâncio C. S. Friaça and Heitor Ernandes

Galaxies 2025, 13(5), 113; https://doi.org/10.3390/galaxies13050113 - 22 Sep 2025

Viewed by 1587

Abstract

Chemical abundances of cobalt (Co; Z = 27) and copper (Cu; Z = 29) in bulge and halo stars are presented and compared with chemical evolution models. The aim is to distinguish if Co and Cu are dominantly produced by neutron-capture or the [...] Read more.

Chemical abundances of cobalt (Co; Z = 27) and copper (Cu; Z = 29) in bulge and halo stars are presented and compared with chemical evolution models. The aim is to distinguish if Co and Cu are dominantly produced by neutron-capture or the alpha-rich freeze-out processes. Neutron-capture can be identified by a secondary behaviour in the [X/Fe] vs. [Fe/H] plot, and alpha-rich freeze-out would give rather a primary behaviour. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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Review

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25 pages, 12660 KB

Open AccessReview

Beta Decays of Heavy Nuclear Species for S-Process Studies

by Kohji Takahashi

Galaxies 2026, 14(2), 34; https://doi.org/10.3390/galaxies14020034 - 16 Apr 2026

Viewed by 98

Abstract

There are some 300 naturally occurring nuclides. In addition, over 3000 radioactive isotopes have become known. The s(low) and r(apid) processes of neutron capture synthesize the nuclides heavier than iron. The synthesis, namely the increase in the atomic numbers Z, is actually [...] Read more.

There are some 300 naturally occurring nuclides. In addition, over 3000 radioactive isotopes have become known. The s(low) and r(apid) processes of neutron capture synthesize the nuclides heavier than iron. The synthesis, namely the increase in the atomic numbers Z, is actually governed by

β

decays. A “flow” of successive neutron captures in the chart of the nuclides is intercepted by a nucleus whose

β

decay half-life is short enough. In this review, I discuss the s-process exclusively. The neutron capture rate to be compared with the

β

decay rate is represented by

λ = n_{n} v_{T} < σ >

, where

n_{n}

is the neutron number density,

v_{T}

is the neutron thermal velocity at the temperature T, and

< σ >

is the Maxwellian averaged (around

v_{T}

) radiative neutron capture cross-section, which depends on the nucleus of interest. The classical analysis of the solar system abundances of nuclides leads to canonical combinations like

n_{n} \sim 10^{8} / {cm}^{3}

and

T \sim 3 \times 10^{8}

K for the s-process. The s-process flow becomes intricate when the neutron capture and

β

decay timescales are comparable, causing a branch of the flow. Subsequently, an evaluation of

β

decay rates is required, which is difficult to do straightforwardly. In this review, I will discuss the historical developments and the current status of predicting

β

decay rates under s-process environments (specified basically by temperature, density, and composition). Those conditions are inaccessible in the laboratory. Embedded in high-temperature environments, even a very massive atomic species could be highly ionized, and its atomic and nuclear excited states could be thermally populated. I will exemplify the consequent difficulties of

β

decay rate evaluations for s-process studies. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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