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An updated picture of pre-solar history from short-lived radioactive isotopes and inferences on the birth of the Sun
Authors:
Benjámin Soós,
Thomas C. L. Trueman,
Andrés Yagüe López,
Lorenzo Roberti,
Maria Lugaro
Abstract:
We examine the origin of the short-lived radionuclides (SLRs, defined as having half-lives between 0.1 and 100 Ma) present in the early Solar System (ESS) by investigating how predictions of their abundances in the interstellar medium (ISM) from steady-state equilibrium relate to their ESS values. For this, we take into account the non-negligible time $t_{\mathrm{iso}}$ elapsed between the isolati…
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We examine the origin of the short-lived radionuclides (SLRs, defined as having half-lives between 0.1 and 100 Ma) present in the early Solar System (ESS) by investigating how predictions of their abundances in the interstellar medium (ISM) from steady-state equilibrium relate to their ESS values. For this, we take into account the non-negligible time $t_{\mathrm{iso}}$ elapsed between the isolation of the pre-solar molecular cloud and the formation of the ESS, during which the SLRs decayed freely. We also consider the alternative scenario in which the pre-solar molecular cloud remained partially mixed with the ISM, with a mixing timescale $t_{\mathrm{mix}}$. We find that the ESS abundances of $^{107}$Pd and $^{182}$Hf produced by \textit{slow} neutron captures (\textit{s}-process), and of $^{53}$Mn and $^{60}$Fe produced by explosive nucleosynthesis, can be consistently explained within these scenarios. Their required $t_{\mathrm{iso}}$ is 9-12 Ma, and their required $t_{\mathrm{mix}}$ is 11-14 Ma (with one potential exception of $t_{\mathrm{mix}}$ = 38 Ma), depending on galactic uncertainties, such as the galactic star formation history and efficiency and the star-to-gas mass ratio. Another \textit{s}-process SLR, $^{205}$Pb has a more uncertain ESS value, and falls within only some of these time values. The same applies to the SLRs produced by the $p$-process ($^{92}$Nb and $^{146}$Sm), depending on the latter's half-life. In agreement with previous studies, we find that the ESS abundances of the \textit{rapid} neutron-capture isotopes ($^{129}$I, $^{244}$Pu, and $^{247}$Cm) and of the most short-lived radionuclides ($^{26}$Al, $^{36}$Cl and $^{41}$Ca) cannot be explained by assuming steady-state equilibrium in the ISM.
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Submitted 1 April, 2026;
originally announced April 2026.
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Galactic chemical evolution with the short-lived isotopes Mn-53, Fe-60, Hf-182, and Pu-244
Authors:
Benjamin Wehmeyer,
Andrés Yagüe López,
Benoit Côté,
Maria K. Pető,
Chiaki Kobayashi,
Maria Lugaro
Abstract:
We run a three-dimensional Galactic chemical evolution (GCE) model to follow the propagation of Mn-53 from supernovae of type Ia (SNIa), Fe-60 from core-collapse supernovae (CCSNe), Hf-182 from intermediate mass stars (IMSs), and Pu-244 from neutron star mergers (NSMs) in the Galaxy. We compare the GCE of these short-lived radioactive isotopes (SLRs) to recent detections on the deep-sea floor. We…
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We run a three-dimensional Galactic chemical evolution (GCE) model to follow the propagation of Mn-53 from supernovae of type Ia (SNIa), Fe-60 from core-collapse supernovae (CCSNe), Hf-182 from intermediate mass stars (IMSs), and Pu-244 from neutron star mergers (NSMs) in the Galaxy. We compare the GCE of these short-lived radioactive isotopes (SLRs) to recent detections on the deep-sea floor. We find that although these SLRs originate from different sites, they often arrive conjointly on Earth.
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Submitted 14 October, 2025;
originally announced October 2025.
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Galactic chemical evolution of short-lived radioactive isotopes produced by explosive nucleosynthesis: $^{60}$Fe and $^{53}$Mn
Authors:
Thomas C. L. Truemam,
Andrés Yagüe López,
Maria Lugaro,
Marco Pignatari
Abstract:
Several short-lived radionuclides (SLRs) are know to have existed in the early Solar System (ESS). These species, which typically decay with half-lives of the order of a few million years, can be used to probe the timescale of events preceding the birth of the Sun. We investigate the ESS origin of $^{53}$Mn, produced by core-collapse (CCSNe) and Type Ia supernovae (SNe Ia), and $^{60}$Fe, produced…
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Several short-lived radionuclides (SLRs) are know to have existed in the early Solar System (ESS). These species, which typically decay with half-lives of the order of a few million years, can be used to probe the timescale of events preceding the birth of the Sun. We investigate the ESS origin of $^{53}$Mn, produced by core-collapse (CCSNe) and Type Ia supernovae (SNe Ia), and $^{60}$Fe, produced exclusively by CCSNe. We model the evolution of the radioactive-to-stable abundance ratios of these SLRs with a galactic chemical evolution (GCE) framework accounting for different supernova yields, SN Ia delay times, and other galactic features $(K)$. A further set of models are calculated assuming that SN Ia did not contribute any $^{53}$Mn to the ESS. The predicted ratios are compared to meteoritic ratios to derive a distribution of solar isolation times that includes uncertainties due to stochastic chemical enrichment and precision of the ESS values. The isolation times are then compared to those of $^{107}$Pd and $^{182}$Hf calculated in previous work. A self-consistent solution can be found within the current uncertainties, especially when using the GCE setups with $K = 1.6$ and 2.3, although the maximum likelihood for the \iso{60}Fe distribution is typically $\sim 4-5$ Myr shorter than for \iso{53}Mn. The predicted \iso{60}Fe/\iso{53}Mn ratio, instead, is completely inconsistent with the ESS value; this could be resolved using a larger fraction of faint CCSNe than usually considered in GCE models.
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Submitted 25 September, 2025;
originally announced September 2025.
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HARD: A Performance Portable Radiation Hydrodynamics Code based on FleCSI Framework
Authors:
Julien Loiseau,
Hyun Lim,
Andrés Yagüe López,
Mammadbaghir Baghirzade,
Shihab Shahriar Khan,
Yoonsoo Kim,
Sudarshan Neopane,
Alexander Strack,
Farhana Taiyebah,
Benjamin K. Bergen
Abstract:
Hydrodynamics And Radiation Diffusion} (HARD) is an open-source application for high-performance simulations of compressible hydrodynamics with radiation-diffusion coupling. Built on the FleCSI (Flexible Computational Science Infrastructure) framework, HARD expresses its computational units as tasks whose execution can be orchestrated by multiple back-end runtimes, including Legion, MPI, and HPX.…
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Hydrodynamics And Radiation Diffusion} (HARD) is an open-source application for high-performance simulations of compressible hydrodynamics with radiation-diffusion coupling. Built on the FleCSI (Flexible Computational Science Infrastructure) framework, HARD expresses its computational units as tasks whose execution can be orchestrated by multiple back-end runtimes, including Legion, MPI, and HPX. Node-level parallelism is delegated to Kokkos, providing a single, portable code base that runs efficiently on laptops, small homogeneous clusters, and the largest heterogeneous supercomputers currently available. To ensure scientific reliability, HARD includes a regression-test suite that automatically reproduces canonical verification problems such as the Sod and LeBlanc shock tubes and the Sedov blast wave, comparing numerical solutions against known analytical results. The project is distributed under an OSI-approved license, hosted on GitHub, and accompanied by reproducible build scripts and continuous integration workflows. This combination of performance portability, verification infrastructure, and community-focused development makes HARD a sustainable platform for advancing radiation hydrodynamics research across multiple domains.
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Submitted 10 September, 2025;
originally announced September 2025.
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The aluminium-26 distribution in a cosmological simulation of a Milky Way-type Galaxy
Authors:
B. Wehmeyer,
C. Kobayashi,
A. Yagüe López,
M. Lugaro
Abstract:
Context. The 1.8 MeV gamma-rays corresponding to the decay of the radioactive isotope Al-26 (with a half-life of 0.72 Myr) have been observed by the SPI detector on the INTEGRAL spacecraft and extensively used as a tracer of star formation and current nucleosynthetic activity in the Milky Way Galaxy. Further information is encoded in the observation related to the higher Al-26 content found in reg…
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Context. The 1.8 MeV gamma-rays corresponding to the decay of the radioactive isotope Al-26 (with a half-life of 0.72 Myr) have been observed by the SPI detector on the INTEGRAL spacecraft and extensively used as a tracer of star formation and current nucleosynthetic activity in the Milky Way Galaxy. Further information is encoded in the observation related to the higher Al-26 content found in regions of the Galaxy with the highest line-of-sight (LoS) velocity relative to an observer located in the Solar System. However, this feature remains unexplained. Aims. We ran a cosmological "zoom-in" chemodynamical simulation of a Milky Way-type galaxy, including the production and decays of radioactive nuclei in a fully self-consistent way. We then analyzed the results to follow the evolution of Al-26 throughout the lifetime of the simulated galaxy to provide a new method for interpreting the Al-26 observations. Methods. We included the massive star sources of Al-26 in the Galaxy and its radioactive decay into a state-of-the-art galactic chemical evolution model, coupled with cosmological growth and hydrodynamics. This approach allowed us to follow the spatial and temporal evolution of the Al-26 content in the simulated galaxy. Results. Our results are in agreement with the observations with respect to the fact that gas particles in the simulation with relatively higher Al-26 content also have the highest LoS velocities. On the other hand, gas particles with relatively lower Al-26 content (i.e., not bright enough to be observed) generally display the lowest LoS velocities. However, this result is not conclusive because the overall rotational velocity of our simulated galaxy is higher than that observed for cold CO gas in the Milky Way Galaxy. Furthermore, we found no significant correlation between gas temperature, rotational velocity, and Al-26 content at any given radius. We also [...]
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Submitted 24 April, 2025;
originally announced April 2025.
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Impact of $\textit{T}$- and $ρ$-dependent decay rates and new (n,$γ$) cross sections on the $\textit{s}$ process in low-mass AGB stars
Authors:
B. Szányi,
A. Yagüe López,
A. I. Karakas,
M. Lugaro
Abstract:
We study the impact of nuclear input related to weak-decay rates and neutron-capture reactions on predictions for the $s$ process in AGB stars. We provide the first database of surface abundances and stellar yields of the isotopes heavier than iron from the $Monash$ models. We run nucleosynthesis calculations with the $Monash$ post-processing code for 7 stellar structure evolution models of low-ma…
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We study the impact of nuclear input related to weak-decay rates and neutron-capture reactions on predictions for the $s$ process in AGB stars. We provide the first database of surface abundances and stellar yields of the isotopes heavier than iron from the $Monash$ models. We run nucleosynthesis calculations with the $Monash$ post-processing code for 7 stellar structure evolution models of low-mass AGB stars with 3 different sets of nuclear input. The reference set has constant decay rates and represents the set used in the previous $Monash$ publications. The second set contains the temperature and density dependence of $β$ decays and electron captures based on the default rates of NETGEN. In the third set, we update 92 neutron-capture rates based on reevaluated experimental cross sections from the ASTRAL. We compare and discuss the predictions of each set relative to each other in terms of isotopic surface abundances and total stellar yields. We also compare results to isotopic ratios measured in presolar stardust SiC grains from AGB stars. The new sets of models resulted in a $\sim$66% solar $s$-process contribution to the $p$-nucleus $\mathrm{^{152}Gd}$, confirming that this isotope is predominantly made by the $s$ process. The nuclear input updates resulted in predictions for the $\mathrm{^{80}Kr/^{82}Kr}$ ratio in the He intershell and surface $\mathrm{^{64}Ni/^{58}Ni}, \mathrm{^{94}Mo/^{96}Mo}$ and $\mathrm{^{137}Ba/^{136}Ba}$ ratios more consistent with the corresponding ratios measured in stardust, however, the new predicted $\mathrm{^{138}Ba/^{136}Ba}$ ratios are higher than the typical values of the stardust SiC grain data. The W isotopic anomalies are in agreement with data from analysis of other meteoritic inclusions. We confirm that the production of $\mathrm{^{176}Lu}$ and $\mathrm{^{205}Pb}$ is affected by too large uncertainties in their decay rates from NETGEN.
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Submitted 11 March, 2025;
originally announced March 2025.
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NYT-Connections: A Deceptively Simple Text Classification Task that Stumps System-1 Thinkers
Authors:
Angel Yahir Loredo Lopez,
Tyler McDonald,
Ali Emami
Abstract:
Large Language Models (LLMs) have shown impressive performance on various benchmarks, yet their ability to engage in deliberate reasoning remains questionable. We present NYT-Connections, a collection of 358 simple word classification puzzles derived from the New York Times Connections game. This benchmark is designed to penalize quick, intuitive "System 1" thinking, isolating fundamental reasonin…
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Large Language Models (LLMs) have shown impressive performance on various benchmarks, yet their ability to engage in deliberate reasoning remains questionable. We present NYT-Connections, a collection of 358 simple word classification puzzles derived from the New York Times Connections game. This benchmark is designed to penalize quick, intuitive "System 1" thinking, isolating fundamental reasoning skills. We evaluated six recent LLMs, a simple machine learning heuristic, and humans across three configurations: single-attempt, multiple attempts without hints, and multiple attempts with contextual hints. Our findings reveal a significant performance gap: even top-performing LLMs like GPT-4 fall short of human performance by nearly 30%. Notably, advanced prompting techniques such as Chain-of-Thought and Self-Consistency show diminishing returns as task difficulty increases. NYT-Connections uniquely combines linguistic isolation, resistance to intuitive shortcuts, and regular updates to mitigate data leakage, offering a novel tool for assessing LLM reasoning capabilities.
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Submitted 25 February, 2025; v1 submitted 2 December, 2024;
originally announced December 2024.
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High-temperature $^{205}$Tl decay clarifies $^{205}$Pb dating in early Solar System
Authors:
G. Leckenby,
R. S. Sidhu,
R. J. Chen,
R. Mancino,
B. Szányi,
M. Bai,
U. Battino,
K. Blaum,
C. Brandau,
S. Cristallo,
T. Dickel,
I. Dillmann,
D. Dmytriiev,
T. Faestermann,
O. Forstner,
B. Franczak,
H. Geissel,
R. Gernhäuser,
J. Glorius,
C. Griffin,
A. Gumberidze,
E. Haettner,
P. -M. Hillenbrand,
A. Karakas,
T. Kaur
, et al. (34 additional authors not shown)
Abstract:
Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth. Among such nuclei whose decay signatures are found in the oldest meteorites, $^{205}$Pb is a powerful example, as it is produced exclusively by slow neutron captures (the s process), with most being synthesized in a…
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Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth. Among such nuclei whose decay signatures are found in the oldest meteorites, $^{205}$Pb is a powerful example, as it is produced exclusively by slow neutron captures (the s process), with most being synthesized in asymptotic giant branch (AGB) stars. However, making accurate abundance predictions for $^{205}$Pb has so far been impossible because the weak decay rates of $^{205}$Pb and $^{205}$Tl are very uncertain at stellar temperatures. To constrain these decay rates, we measured for the first time the bound-state $β^-$ decay of fully ionized $^{205}$Tl$^{81+}$, an exotic decay mode that only occurs in highly charged ions. The measured half-life is 4.7 times longer than the previous theoretical estimate and our 10% experimental uncertainty has eliminated the main nuclear-physics limitation. With new, experimentally backed decay rates, we used AGB stellar models to calculate $^{205}$Pb yields. Propagating those yields with basic galactic chemical evolution (GCE) and comparing with the $^{205}$Pb/$^{204}$Pb ratio from meteorites, we determined the isolation time of solar material inside its parent molecular cloud. We find positive isolation times that are consistent with the other s-process short-lived radioactive nuclei found in the early Solar System. Our results reaffirm the site of the Sun's birth as a long-lived, giant molecular cloud and support the use of the $^{205}$Pb--$^{205}$Tl decay system as a chronometer in the early Solar System.
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Submitted 13 November, 2024;
originally announced November 2024.
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Barium stars as tracers of s-process nucleosynthesis in AGB stars III. Systematic deviations from the AGB models
Authors:
B. Világos,
B. Cseh,
A. Yagüe López,
M. Joyce,
A. Karakas,
G. Tagliente,
M. Lugaro
Abstract:
Barium (Ba) stars help to verify asymptotic giant branch (AGB) star nucleosynthesis models since they experienced pollution from an AGB binary companion and thus their spectra carry the signatures of the slow neutron capture process (s process). For 180 Ba stars, we searched for AGB stellar models that match the observed abundance patterns. We employed three machine learning algorithms as classifi…
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Barium (Ba) stars help to verify asymptotic giant branch (AGB) star nucleosynthesis models since they experienced pollution from an AGB binary companion and thus their spectra carry the signatures of the slow neutron capture process (s process). For 180 Ba stars, we searched for AGB stellar models that match the observed abundance patterns. We employed three machine learning algorithms as classifiers: a Random Forest method, developed for this work, and the two classifiers used in our previous study. We studied the statistical behaviour of the s-process elements in the observational sample to investigate if the AGB models systematically under- or overpredict the abundances observed in the Ba stars and show the results in the form of violin plots of the residuals between spectroscopic abundances and model predictions. We find a significant trend in the residuals that implies an underproduction of the elements Nb, Mo, and Ru in the models relative to the observations. This may originate from a process (e.g. the intermediate neutron-capture process, i process) at the metallicity of the Ba stars not yet included in the AGB models. Correlations are found between the residuals of these elements, suggesting a common origin for the deviations. In addition, there is a weak metallicity dependence of their residuals. The s-process temperatures derived with the [Zr/Fe] - [Nb/Fe] thermometer have an unrealistic value for the majority of our stars. The most likely explanation is that at least a fraction of these elements are not produced in a steady-state s process, and instead may be due to processes not included in the AGB models. The mass distribution of the identified models confirms that our sample of Ba stars was polluted by low-mass AGB stars. Most of the matching AGB models require low accreted mass, but a few systems with high accreted mass are needed to explain the observations. (abridged)
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Submitted 29 May, 2024;
originally announced May 2024.
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Inhomogeneous enrichment of radioactive nuclei in the Galaxy: Deposition of live Mn-53, Fe-60, Hf-182, and Pu-244 into deep-sea archives. Surfing the wave?
Authors:
Benjamin Wehmeyer,
Andrés Yagüe López,
Benoit Côté,
Maria K. Pető,
Chiaki Kobayashi,
Maria Lugaro
Abstract:
While modelling the galactic chemical evolution (GCE) of stable elements provides insights to the formation history of the Galaxy and the relative contributions of nucleosynthesis sites, modelling the evolution of short-lived radioisotopes (SLRs) can provide supplementary timing information on recent nucleosynthesis. To study the evolution of SLRs, we need to understand their spatial distribution.…
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While modelling the galactic chemical evolution (GCE) of stable elements provides insights to the formation history of the Galaxy and the relative contributions of nucleosynthesis sites, modelling the evolution of short-lived radioisotopes (SLRs) can provide supplementary timing information on recent nucleosynthesis. To study the evolution of SLRs, we need to understand their spatial distribution. Using a 3-dimensional GCE model, we investigated the evolution of four SLRs: Mn-53, Fe-60, Hf-182, and Pu-244 with the aim of explaining detections of recent (within the last $\approx$1-20 Myr) deposition of live Mn-53, Fe-60, and Pu-244 of extrasolar origin into deep-sea reservoirs. We find that core-collapse supernovae (CCSNe) are the dominant propagation mechanism of SLRs in the Galaxy. This results in the simultaneously arrival of these four SLRs on Earth, although they could have been produced in different astrophysical sites, which can explain why live extrasolar Mn-53, Fe-60, and Pu-244 are found within the same, or similar, layers of deep-sea sediments. We predict that Hf-182 should also be found in such sediments at similar depths.
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Submitted 21 February, 2023; v1 submitted 11 January, 2023;
originally announced January 2023.
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Barium stars as tracers of s-process nucleosynthesis in AGB stars II. Using machine learning techniques on 169 stars
Authors:
J. W. den Hartogh,
A. Yagüe López,
B. Cseh,
M. Pignatari,
B. Világos,
M. P. Roriz,
C. B. Pereira,
N. A. Drake,
S. Junqueira,
M. Lugaro
Abstract:
We aim to analyse the abundance pattern of 169 Barium (Ba) stars, using machine learning techniques and the AGB final surface abundances predicted by Fruity and Monash stellar models. We developed machine learning algorithms that use the abundance pattern of Ba stars as input to classify the initial mass and metallicity of its companion star using stellar model predictions. We use two algorithms:…
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We aim to analyse the abundance pattern of 169 Barium (Ba) stars, using machine learning techniques and the AGB final surface abundances predicted by Fruity and Monash stellar models. We developed machine learning algorithms that use the abundance pattern of Ba stars as input to classify the initial mass and metallicity of its companion star using stellar model predictions. We use two algorithms: the first exploits neural networks to recognise patterns and the second is a nearest-neighbour algorithm, which focuses on finding the AGB model that predicts final surface abundances closest to the observed Ba star values. In the second algorithm we include the error bars and observational uncertainties to find the best fit model. The classification process is based on the abundances of Fe, Rb, Sr, Zr, Ru, Nd, Ce, Sm, and Eu. We selected these elements by systematically removing s-process elements from our AGB model abundance distributions, and identifying those whose removal has the biggest positive effect on the classification. We excluded Nb, Y, Mo, and La. Our final classification combines the output of both algorithms to identify for each Ba star companion an initial mass and metallicity range. With our analysis tools we identify the main properties for 166 of the 169 Ba stars in the stellar sample. The classifications based on both stellar sets of AGB final abundances show similar distributions, with an average initial mass of M = 2.23 MSun and 2.34 MSun and an average [Fe/H] = -0.21 and -0.11, respectively. We investigated why the removal of Nb, Y, Mo, and La improves our classification and identified 43 stars for which the exclusion had the biggest effect. We show that these stars have statistically significant different abundances for these elements compared to the other Ba stars in our sample. We discuss the possible reasons for these differences in the abundance patterns.
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Submitted 7 December, 2022;
originally announced December 2022.
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Enrichment of the Galactic disc with neutron-capture elements: Gd, Dy, and Th
Authors:
T. Mishenina,
M. Pignatari,
T. Gorbaneva,
B. Cote,
A. Yague Lopez,
F. -K. Thielemann,
C. Soubiran
Abstract:
The study of the origin of heavy elements is one of the main goals of nuclear astrophysics. In this paper, we present new observational data for the heavy $r$-process elements gadolinium (Gd, Z=64), dysprosium (Dy, Z=66) and thorium (Th, Z=90) in a sample of 276 Galactic disc stars ( --1.0$<$[Fe/H]$<$+0.3). The stellar spectra have a high resolution of 42,000 and 75,000, and the signal-to-noise ra…
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The study of the origin of heavy elements is one of the main goals of nuclear astrophysics. In this paper, we present new observational data for the heavy $r$-process elements gadolinium (Gd, Z=64), dysprosium (Dy, Z=66) and thorium (Th, Z=90) in a sample of 276 Galactic disc stars ( --1.0$<$[Fe/H]$<$+0.3). The stellar spectra have a high resolution of 42,000 and 75,000, and the signal-to-noise ratio higher than 100. The LTE abundances of Gd, Dy and Th have been determined by comparing the observed and synthetic spectra for three Gd lines (149 stars), four Dy lines (152 stars) and the Th line at 4019.13 A (170 stars). For about 70% of the stars in our sample Gd and Dy are measured for the first time, and Th for 95% of the stars. Typical errors vary from 0.07 to 0.16 dex. This paper provides the first extended set of Th observations in the Milky Way disc. Together with europium (Eu, Z = 63) data from our previous studies, we have compared these new observations with nucleosynthesis predictions and Galactic Chemical Evolution simulations. We confirm that [Gd/Fe] and [Dy/Fe] show the same behavior of Eu. We study with GCE simulations the evolution of [Th/Fe] in comparison with [Eu/Fe], showing that unlike Eu either the Th production is metallicity dependent in case of a unique source of the r-process in the Galaxy, or the frequency of the Th-rich r-process source is decreasing with the increasing of [Fe/H].
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Submitted 24 August, 2022;
originally announced August 2022.
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Origin of Plutonium-244 in the Early Solar System
Authors:
Maria Lugaro,
Andrés Yagüe López,
Benjámin Soós,
Benoit Côté,
Mária Pető,
Nicole Vassh,
Benjamin Wehmeyer,
Marco Pignatari
Abstract:
We investigate the origin in the early Solar System of the short-lived radionuclide 244Pu (with a half life of 80 Myr) produced by the rapid (r) neutron-capture process. We consider two large sets of r-process nucleosynthesis models and analyse if the origin of 244Pu in the ESS is consistent with that of the other r and slow (s) neutron-capture process radioactive nuclei. Uncertainties on the r-pr…
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We investigate the origin in the early Solar System of the short-lived radionuclide 244Pu (with a half life of 80 Myr) produced by the rapid (r) neutron-capture process. We consider two large sets of r-process nucleosynthesis models and analyse if the origin of 244Pu in the ESS is consistent with that of the other r and slow (s) neutron-capture process radioactive nuclei. Uncertainties on the r-process models come from both the nuclear physics input and the astrophysical site. The former strongly affects the ratios of isotopes of close mass (129I/127I, 244Pu/238U, and 247Pu/235U). The 129I/247Cm ratio, instead, which involves isotopes of a very different mass, is much more variable than those listed above and is more affected by the physics of the astrophysical site. We consider possible scenarios for the evolution of the abundances of these radioactive nuclei in the galactic interstellar medium and verify under which scenarios and conditions solutions can be found for the origin of 244Pu that are consistent with the origin of the other isotopes. Solutions are generally found for all the possible different regimes controlled by the interval ($δ$) between additions from the source to the parcel of interstellar medium gas that ended up in the Solar System, relative to decay timescales. If r-process ejecta in interstellar medium are mixed within a relatively small area (leading to a long $δ$), we derive that the last event that explains the 129I and 247Cm abundances in the early Solar System can also account for the abundance of 244Pu. Due to its longer half life, however, 244Pu may have originated from a few events instead of one only. If r-process ejecta in interstellar medium are mixed within a relatively large area (leading to a short $δ$), we derive that the time elapsed from the formation of the molecular cloud to the formation of the Sun was 9-16 Myr.
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Submitted 3 August, 2022;
originally announced August 2022.
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The RADIOSTAR Project
Authors:
Maria Lugaro,
Benoit Côté,
Marco Pignatari,
Andrés Yagüe López,
Hannah Brinkman,
Borbála Cseh,
Jacqueline Den Hartogh,
Carolyn Louise Doherty,
Amanda Irene Karakas,
Chiaki Kobayashi,
Thomas Lawson,
Mária Pető,
Benjámin Soós,
Thomas Trueman,
Blanka Világos
Abstract:
Radioactive nuclei are the key to understanding the circumstances of the birth of our Sun because meteoritic analysis has proven that many of them were present at that time. Their origin, however, has been so far elusive. The ERC-CoG-2016 RADIOSTAR project is dedicated to investigating the production of radioactive nuclei by nuclear reactions inside stars, their evolution in the Milky Way Galaxy,…
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Radioactive nuclei are the key to understanding the circumstances of the birth of our Sun because meteoritic analysis has proven that many of them were present at that time. Their origin, however, has been so far elusive. The ERC-CoG-2016 RADIOSTAR project is dedicated to investigating the production of radioactive nuclei by nuclear reactions inside stars, their evolution in the Milky Way Galaxy, and their presence in molecular clouds. So far, we have discovered that: (i) radioactive nuclei produced by slow ($^{107}$Pd and $^{182}$Hf) and rapid ($^{129}$I and $^{247}$Cm) neutron captures originated from stellar sources - asymptotic giant branch (AGB) stars and compact binary mergers, respectively - within the galactic environment that predated the formation of the molecular cloud where the Sun was born; (ii) the time that elapsed from the birth of the cloud to the birth of the Sun was of the order of 10$^7$ years, and (iii) the abundances of the very short-lived nuclei $^{26}$Al, $^{36}$Cl, and $^{41}$Ca can be explained by massive star winds in single or binary systems, if these winds directly polluted the early Solar System. Our current and future work, as required to finalise the picture of the origin of radioactive nuclei in the Solar System, involves studying the possible origin of radioactive nuclei in the early Solar System from core-collapse supernovae, investigating the production of $^{107}$Pd in massive star winds, modelling the transport and mixing of radioactive nuclei in the galactic and molecular cloud medium, and calculating the galactic chemical evolution of $^{53}$Mn and $^{60}$Fe and of the p-process isotopes $^{92}$Nb and $^{146}$Sm.
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Submitted 16 February, 2022;
originally announced February 2022.
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Galactic Chemical Evolution of Radioactive Isotopes with an s-process Contribution
Authors:
T. C. L. Trueman,
B. Côté,
A. Yagüe López,
J. den Hartogh,
M. Pignatari,
B. Soós,
A. I. Karakas,
M. Lugaro
Abstract:
Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives $0.1-100$ Myr existed in the early Solar System (ESS). We investigate the ESS origin of $^{107}$Pd, $^{135}$Cs, and $^{182}$Hf, which are produced by $slow$ neutron captures (the $s$-process) in asymptotic giant branch (AGB) stars. We modelled the galactic abundances of these SLRs u…
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Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives $0.1-100$ Myr existed in the early Solar System (ESS). We investigate the ESS origin of $^{107}$Pd, $^{135}$Cs, and $^{182}$Hf, which are produced by $slow$ neutron captures (the $s$-process) in asymptotic giant branch (AGB) stars. We modelled the galactic abundances of these SLRs using the OMEGA+ galactic chemical evolution (GCE) code and two sets of mass- and metallicity-dependent AGB nucleosynthesis yields (Monash and FRUITY). Depending on the ratio of the mean life $τ$ of the SLR to the average length of time between the formation of AGB progenitor $γ$, we calculate timescales relevant for the birth of the Sun. If $τ/γ\gtrsim2$, we predict self-consistent isolation times between 9 and 26 Myr by decaying the GCE predicted $^{107}$Pd/$^{108}$Pd, $^{135}$Cs/$^{133}$Cs, and $^{182}$Hf/$^{180}$Hf ratios to their respective ESS ratios. The predicted $^{107}$Pd/$^{182}$Hf ratio indicates that our GCE models are missing $9-73\%$ of $^{107}$Pd and $^{108}$Pd in the ESS. This missing component may have come from AGB stars of higher metallicity than those that contributed to the ESS in our GCE code. If $τ/γ\lesssim0.3$, we calculate instead the time ($T_{\rm LE}$) from the last nucleosynthesis event that added the SLRs into the presolar matter to the formation of the oldest solids in the ESS. For the 2 M$_\odot$, $Z=0.01$ Monash model we find a self-consistent solution of $T_{\rm LE}=25.5$ Myr.
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Submitted 21 October, 2021;
originally announced October 2021.
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First models of s process in AGB stars of solar metallicity for the stellar evolutionary code ATON with a novel stable explicit numerical solver
Authors:
A. Yagüe López,
D. A. García-Hernández,
P. Ventura,
C. L. Doherty,
J. W. den Hartogh,
S. W. Jones,
M. Lugaro
Abstract:
Aims. We describe the first s-process post-processing models for asymptotic giant branch (AGB) stars of masses 3, 4 and 5 M at solar metallicity (Z=0.018) computed using the input from the stellar evolutionary code aton. Methods. The models are computed with the new code snuppat(S-process NUcleosynthesis Post-Processing code for aton), including an advective scheme for the convective overshoot tha…
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Aims. We describe the first s-process post-processing models for asymptotic giant branch (AGB) stars of masses 3, 4 and 5 M at solar metallicity (Z=0.018) computed using the input from the stellar evolutionary code aton. Methods. The models are computed with the new code snuppat(S-process NUcleosynthesis Post-Processing code for aton), including an advective scheme for the convective overshoot that leads to the formation of the main neutron source, 13C. Each model is post-processed with 3 different values of the free overshoot parameter. Included in the code snuppat is the novel Patankar-Euler-Deflhard explicit numerical solver, that we use to solve the nuclear network system of differential equations. Results. The results are compared to those from other s-process nucleosynthesis codes (Monash,fruity, and NuGrid), as well as observations of s-process enhancement in AGB stars, planetary nebulae, and barium stars. This comparison shows that the relatively high abundance of12C in the He-rich intershell in aton results in as-process abundance pattern that favours the second over the first s-process peak for all the masses explored. Also, our choice of an advective as opposed to diffusive numerical scheme for the convective overshoot results in significants-process nucleosynthesis also for the 5 M models, which may be in contradiction with observations.
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Submitted 15 October, 2021;
originally announced October 2021.
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The stellar beta-decay rate of 134Cs and its impact on the Barium nucleosynthesis in the s process
Authors:
Kuo-Ang Li,
Chong Qi,
Maria Lugaro,
Andrés Yagüe López,
Amanda I. Karakas,
Jacqueline den Hartogh,
Bing-Shui Gao,
Xiao-Dong Tang
Abstract:
We have calculated the stellar $β$-decay rate of the important s-process branching point ${}^{134}$Cs based on the state of the art shell model calculations. At typical $s$-process temperatures ($T\sim$ 0.2-0.3 GK), our new rate is one order of magnitude lower than the widely-used rate from Takahashi and Yokoi (hereafter TY87). The impact on the nucleosynthesis in AGB stars is investigated with va…
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We have calculated the stellar $β$-decay rate of the important s-process branching point ${}^{134}$Cs based on the state of the art shell model calculations. At typical $s$-process temperatures ($T\sim$ 0.2-0.3 GK), our new rate is one order of magnitude lower than the widely-used rate from Takahashi and Yokoi (hereafter TY87). The impact on the nucleosynthesis in AGB stars is investigated with various masses and metallicities. Our new decay rate leads to an overall decrease in the ${}^{134}$Ba/${}^{136}$Ba ratio, and well explains the measured ratio in meteorities without introducing the $i$ process. We also derive the elapsed time from the last AGB nucleosynthetic event that polluted the early Solar System to be $>$28 Myr based on the ${}^{135}$Cs/${}^{133}$Cs ratio, which is consistent with the elapsed times derived from ${}^{107}$Pd and ${}^{182}$Hf. The $s$-process abundance sum of ${}^{135}$Ba and ${}^{135}$Cs is found to increase, resulting in a smaller $r$-process contribution of ${}^{135}$Ba in the Solar System.
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Submitted 29 September, 2021; v1 submitted 24 September, 2021;
originally announced September 2021.
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The Radioactive Nuclei $^{\textbf{26}}$Al and $^{\textbf{60}}$Fe in the Cosmos and in the Solar System
Authors:
Roland Diehl,
Maria Lugaro,
Alexander Heger,
Andre Sieverding,
Xiaodong Tang,
KuoAng Li,
Ertao Li,
Carolyn L. Doherty,
Martin G. H. Krause,
Anton Wallner,
Nikos Prantzos,
Hannah E. Brinkman,
Jaqueline W. den Hartogh,
Benjamin Wehmeyer,
Andrés Yagüe López,
Moritz M. M. Pleintinger,
Projjval Banerjee,
Wei Wang
Abstract:
The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and of this matter cycle requires the understanding of the physics of nuclear reactions, of the c…
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The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and of this matter cycle requires the understanding of the physics of nuclear reactions, of the conditions at which the nuclear reactions are activated inside the stars and stellar explosions, of the stellar ejection mechanisms through winds and explosions, and of the transport of the ejecta towards the next cycle, from hot plasma to cold, star-forming gas. Due to the long timescales of stellar evolution, and because of the infrequent occurrence of stellar explosions, observational studies are challenging. Due to their radioactive lifetime of million years, the 26Al and 60Fe isotopes are suitable to characterise simultaneously the processes of nuclear fusion reactions and of interstellar transport. We describe and discuss the nuclear reactions involved in the production and destruction of 26Al and 60Fe, the key characteristics of the stellar sites of their nucleosynthesis and their interstellar journey after ejection from the nucleosynthesis sites. We connect the theoretical astrophysical aspects to the variety of astronomical messengers, from stardust and cosmic-ray composition measurements, through observation of gamma rays produced by radioactivity, to material deposited in deep-sea ocean crusts and to the inferred composition of the first solids that have formed in the Solar System. We show that considering measurements of the isotopic ratio of 26Al to 60Fe eliminate some of the unknowns when interpreting astronomical results, and discuss the lessons learned from these two isotopes on cosmic chemical evolution.
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Submitted 5 October, 2021; v1 submitted 17 September, 2021;
originally announced September 2021.
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Gas and dust from extremely metal-poor AGB stars
Authors:
P. Ventura,
F. Dell'Agli,
D. Romano,
S. Tosi,
M. Limongi,
A. Chieffi,
M. Castellani,
M. Tailo,
M. Lugaro,
E. Marini,
A. Yague Lopez
Abstract:
We study the evolution of extremely metal-poor AGB stars, with metallicities down to [Fe/H]=-5, to understand the main evolutionary properties, the efficiency of the processes able to alter their surface chemical composition and to determine the gas and dust yields. We calculate two sets of evolutionary sequences of stars in the 1-7.5Msun mass range, evolved from the pre-main sequence to the end o…
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We study the evolution of extremely metal-poor AGB stars, with metallicities down to [Fe/H]=-5, to understand the main evolutionary properties, the efficiency of the processes able to alter their surface chemical composition and to determine the gas and dust yields. We calculate two sets of evolutionary sequences of stars in the 1-7.5Msun mass range, evolved from the pre-main sequence to the end of the AGB phase. To explore the extremely metal-poor chemistries we adopted the metallicities Z=3x10^{-5} and Z=3x10^{-7} which correspond, respectively to [Fe/H]=-3 and [Fe/H]=-5. The results from stellar evolution modelling are used to calculate the yields of the individual chemical species. We also modelled dust formation in the wind, to determine the dust produced by these objects. The evolution of AGB stars in the extremely metal-poor domain explored here proves tremendously sensitive to the initial mass of the star. M<2Msun stars experience several third dredge-up events, which favour the gradual surface enrichment of C12 and the formation of significant quantities of carbonaceous dust, of the order of 0.01Msun. The C13 and nitrogen yiel are found to be significantly smaller than in previous explorations of low-mass, metal-poor AGB stars, owing to the weaker proton ingestion episodes experienced during the initial AGB phases. M>5Msun stars experience hot bottom burning and their surface chemistry reflects the equilibria of a very advanced proton-capture nucleosynthesis; little dust production takes place in their wind. Intermediate mass stars experience both third dredge-up and hot bottom burning: they prove efficient producers of nitrogen, which is formed by proton captures on C12 nuclei of primary origin dredged-up from the internal regions.
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Submitted 10 August, 2021;
originally announced August 2021.
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Monte Carlo Investigation of the Ratios of Short-Lived Radioactive Isotopes in the Interstellar Medium
Authors:
A. Yagüe López,
B. Côté,
M. Lugaro
Abstract:
Short-lived radioactive nuclei (SLR) with mean lives below 100 Myr provide us with unique insights into current galactic nucleosynthetic events, as well as events that contributed to the material of our Solar System more that 4.6 Gyr ago. Here we present a statistical analysis of the ratios of these radioactive nuclei at the time of early Solar System (ESS) using both analytical derivations and Mo…
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Short-lived radioactive nuclei (SLR) with mean lives below 100 Myr provide us with unique insights into current galactic nucleosynthetic events, as well as events that contributed to the material of our Solar System more that 4.6 Gyr ago. Here we present a statistical analysis of the ratios of these radioactive nuclei at the time of early Solar System (ESS) using both analytical derivations and Monte Carlo methods. We aim to understand the interplay between the production frequency and the mean lives of these isotopes, and its impact on their theoretically predicted ratios in the interstellar medium (ISM). We find that when the ratio of two SRLs, instead of the ratios of each single SLR relative to its stable or long-lived isotope, is considered, not only the uncertainties related to the galactic chemical evolution of the stable isotope are completely eliminated, but also the statistical uncertainties are much lower. We identify four ratios, 247Cm/129I, 107Pd/182Hf, 97Tc/98Tc, and 53Mn/97Tc, that have the potential to provide us with new insights into the r-, s-, and p-process nucleosynthesis at the time of the formation of the Sun, and need to be studied using variable stellar yields. Additionally, the latter two ratios need to be better determined in the ESS to allow us to fully exploit them to investigate the galactic sites of the p process.
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Submitted 19 May, 2021;
originally announced May 2021.