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Articles de revues sur le sujet « Stellar nucleosynthesi »

Auteur : Grafiati
Publié le 9 mars 2023
Mis à jour le 10 mars 2023

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1

Ryan, Sean G. « Big Bang Nucleosynthesis, Population III, and Stellar Genetics in the Galactic Halo ». Publications of the Astronomical Society of Australia 19, no 2 (2002) : 238–45. http://dx.doi.org/10.1071/as01067.

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AbstractThe diverse isotopic and elemental signatures produced in different nucleosynthetic sites are passed on to successive generations of stars. By tracing these chemical signatures back through the stellar populations of the Galaxy, it is possible to unravel its nucleosynthetic history and even to study stars which are now extinct. This review considers recent applications of ‘stellar genetics’ to examine the earliest episodes of nucleosynthesis in the universe, in Population iii stars and the Big Bang.
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2

Doherty, Carolyn, John Lattanzio, George Angelou, Simon W. Campbell, Ross Church, Thomas Constantino, Sergio Cristallo et al. « Monash Chemical Yields Project (Monχey) Element production in low- and intermediate-mass stars ». Proceedings of the International Astronomical Union 11, A29B (août 2015) : 164–65. http://dx.doi.org/10.1017/s1743921316004725.

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AbstractThe Monχey project will provide a large and homogeneous set of stellar yields for the low- and intermediate- mass stars and has applications particularly to galactic chemical evolution modelling. We describe our detailed grid of stellar evolutionary models and corresponding nucleosynthetic yields for stars of initial mass 0.8 M⊙ up to the limit for core collapse supernova (CC-SN) ≈ 10 M⊙. Our study covers a broad range of metallicities, ranging from the first, primordial stars (Z = 0) to those of super-solar metallicity (Z = 0.04). The models are evolved from the zero-age main-sequence until the end of the asymptotic giant branch (AGB) and the nucleosynthesis calculations include all elements from H to Bi. A major innovation of our work is the first complete grid of heavy element nucleosynthetic predictions for primordial AGB stars as well as the inclusion of extra-mixing processes (in this case thermohaline) during the red giant branch. We provide a broad overview of our results with implications for galactic chemical evolution as well as highlight interesting results such as heavy element production in dredge-out events of super-AGB stars. We briefly introduce our forthcoming web-based database which provides the evolutionary tracks, structural properties, internal/surface nucleosynthetic compositions and stellar yields. Our web interface includes user- driven plotting capabilities with output available in a range of formats. Our nucleosynthetic results will be available for further use in post processing calculations for dust production yields.
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Salpeter, Edwin E. « Stellar nucleosynthesis ». Reviews of Modern Physics 71, no 2 (1 mars 1999) : S220—S222. http://dx.doi.org/10.1103/revmodphys.71.s220.

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Weiss, A. « Stellar nucleosynthesis ». Physica Scripta T133 (1 janvier 2008) : 014025. http://dx.doi.org/10.1088/0031-8949/2008/t133/014025.

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5

Vescovi, Diego. « Mixing and Magnetic Fields in Asymptotic Giant Branch Stars in the Framework of FRUITY Models ». Universe 8, no 1 (28 décembre 2021) : 16. http://dx.doi.org/10.3390/universe8010016.

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In the last few years, the modeling of asymptotic giant branch (AGB) stars has been much investigated, both focusing on nucleosynthesis and stellar evolution aspects. Recent advances in the input physics required for stellar computations made it possible to construct more accurate evolutionary models, which are an essential tool to interpret the wealth of available observational and nucleosynthetic data. Motivated by such improvements, the FUNS stellar evolutionary code has been updated. Nonetheless, mixing processes occurring in AGB stars’ interiors are currently not well-understood. This is especially true for the physical mechanism leading to the formation of the 13C pocket, the major neutron source in low-mass AGB stars. In this regard, post-processing s-process models assuming that partial mixing of protons is induced by magneto-hydrodynamics processes were shown to reproduce many observations. Such mixing prescriptions have now been implemented in the FUNS code to compute stellar models with fully coupled nucleosynthesis. Here, we review the new generation of FRUITY models that include the effects of mixing triggered by magnetic fields by comparing theoretical findings with observational constraints available either from the isotopic analysis of trace-heavy elements in presolar grains or from carbon AGB stars and Galactic open clusters.
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Gil-Pons, P., C. L. Doherty, J. Gutiérrez, S. W. Campbell, L. Siess et J. C. Lattanzio. « Nucleosynthetic yields of Z = 10−5 intermediate-mass stars ». Astronomy & ; Astrophysics 645 (21 décembre 2020) : A10. http://dx.doi.org/10.1051/0004-6361/201937264.

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Context. Observed abundances of extremely metal-poor stars in the Galactic halo hold clues for understanding the ancient universe. Interpreting these clues requires theoretical stellar models in a wide range of masses in the low-metallicity regime. The existing literature is relatively rich with extremely metal-poor massive and low-mass stellar models. However, relatively little information is available on the evolution of intermediate-mass stars of Z ≲ 10−5, and the impact of the uncertain input physics on the evolution and nucleosynthesis has not yet been systematically analysed. Aims. We aim to provide the nucleosynthetic yields of intermediate-mass Z = 10−5 stars between 3 and 7.5 M⊙, and quantify the effects of the uncertain wind rates. We expect these yields could eventually be used to assess the contribution to the chemical inventory of the early universe, and to help interpret abundances of selected C-enhanced extremely metal-poor (CEMP) stars. Methods. We compute and analyse the evolution of surface abundances and nucleosynthetic yields of Z = 10−5 intermediate-mass stars from their main sequence up to the late stages of their thermally pulsing (Super) AGB phase, with different prescriptions for stellar winds. We use the postprocessing code MONSOON to compute the nucleosynthesis based on the evolution structure obtained with the Monash-Mount Stromlo stellar evolution code MONSTAR. By comparing our models and others from the literature, we explore evolutionary and nucleosynthetic trends with wind prescriptions and with initial metallicity (in the very low-Z regime). We also compare our nucleosynthetic yields to observations of CEMP-s stars belonging to the Galactic halo. Results. The yields of intermediate-mass extremely metal-poor stars reflect the effects of very deep or corrosive second dredge-up (for the most massive models), superimposed with the combined signatures of hot-bottom burning and third dredge-up. Specifically, we confirm the reported trend that models with initial metallicity Zini ≲ 10−3 give positive yields of 12C, 15N, 16O, and 26Mg. The 20Ne, 21Ne, and 24Mg yields, which were reported to be negative at Zini ≳ 10−4, become positive for Z = 10−5. The results using two different prescriptions for mass-loss rates differ widely in terms of the duration of the thermally pulsing (Super) AGB phase, overall efficiency of the third dredge-up episode, and nucleosynthetic yields. We find that the most efficient of the standard wind rates frequently used in the literature seems to favour agreement between our yield results and observational data. Regardless of the wind prescription, all our models become N-enhanced EMP stars.
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Karinkuzhi, D., S. Van Eck, A. Jorissen, S. Goriely, L. Siess, T. Merle, A. Escorza et al. « When binaries keep track of recent nucleosynthesis ». Proceedings of the International Astronomical Union 14, S343 (août 2018) : 438–40. http://dx.doi.org/10.1017/s1743921318006567.

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AbstractWe determine Zr and Nb elemental abundances in barium stars to probe the operation temperature of the s-process that occurred in the companion asymptotic giant branch (AGB) stars. Along with Zr and Nb, we derive the abundances of a large number of heavy elements. They provide constraints on the s-process operation temperature and therefore on the s-process neutron source. The results are then compared with stellar evolution and nucleosynthesis models. We compare the nucleosynthetic profile of the present sample stars with those of CEMP-s, CEMP-rs and CEMP-r stars. One barium star of our sample is potentially identified as the highest-metallicity CEMP-rs star yet discovered.
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8

AOKI, Wako, et Nobuyuki IWAMOTO. « Stellar Evolution and Nucleosynthesis ». Journal of Plasma and Fusion Research 79, no 9 (2003) : 871–77. http://dx.doi.org/10.1585/jspf.79.871.

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Ryde, Nils, et Graham Harper. « Observing early stellar nucleosynthesis ». Nature Astronomy 5, no 12 (15 novembre 2021) : 1212–13. http://dx.doi.org/10.1038/s41550-021-01510-0.

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Truran, James W. « The Oldest Stars as Tracers of Heavy Element Formation at Early Epochs ». Symposium - International Astronomical Union 204 (2001) : 333–34. http://dx.doi.org/10.1017/s0074180900226247.

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Elemental abundance patterns in very metal-poor halo field stars and globular cluster stars play a crucial role both in guiding theoretical models of nucleosynthesis and in providing constraints upon the early star formation and concomitant nucleosynthesis history of our Galaxy. The abundance patterns characterizing the oldest and most metal deficient stars ([Fe/H] ≤ −3) are entirely consistent with their being products of metal-poor massive stars of lifetimes τ ≤ 108years. This includes both the elevated abundances of thealpha-elements (O, Mg, Si, S, Ca, and Ti) relative to iron-peak elements and the dominance of r-process elements over s-process elements. The nucleosynthetic contributions of lower mass AGB stars of longer lifetimes (τ ≈ 109years) begin to appear at metallicities [Fe/H] ≈ −2.5, while clear evidence for iron-peak nuclei produced in supernovae Ia (τ ≥ 1-2x109years?) does not appear until metallicities approaching [Fe/H] ~ −1. Similar trends are also suggested by abundances determined for gas clouds at high redshifts. We review the manner in which a knowledge of the abundances of the stellar and gas components of early populations, as a function of [Fe/H], time, and/or redshift, can be used to set constraints on their star formation and nucleosynthesis histories.
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11

Aliotta, M., R. Buompane, M. Couder, A. Couture, R. J. deBoer, A. Formicola, L. Gialanella et al. « The status and future of direct nuclear reaction measurements for stellar burning ». Journal of Physics G : Nuclear and Particle Physics 49, no 1 (25 novembre 2021) : 010501. http://dx.doi.org/10.1088/1361-6471/ac2b0f.

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Abstract The study of stellar burning began just over 100 years ago. Nonetheless, we do not yet have a detailed picture of the nucleosynthesis within stars and how nucleosynthesis impacts stellar structure and the remnants of stellar evolution. Achieving this understanding will require precise direct measurements of the nuclear reactions involved. This report summarizes the status of direct measurements for stellar burning, focusing on developments of the last couple of decades, and offering a prospectus of near-future developments.
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12

Norris, John E. « Stellar chemical evolution ». Symposium - International Astronomical Union 189 (1997) : 407–16. http://dx.doi.org/10.1017/s007418090011695x.

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One of the major achievements of astrophysics has been the demonstration that most of the chemical elements have been synthesized in stars: nucleosynthesis calculations of homogeneous and inhomogeneous big bang cosmologies show that, in comparison with the most metal-poor stars currently known, essentially no elements heavier than B existed at the era of decoupling (see e.g. Wagoner, Fowler, & Hoyle 1967; Kajino, Mathews, & Fuller 1990). Following the pioneering work on stellar nucleosynthesis by Hoyle (1946), the basic precepts and the role of stars was set down in the classic papers of Burbidge et al. (1957) and Cameron (1957), and the ensuing decades have produced a vast body of theoretical and observational effort to more fully understand the details of the process.
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Spite, Monique, et François Spite. « Li isotopes in metal-poor halo dwarfs : a more and more complicated story ». Proceedings of the International Astronomical Union 5, S268 (novembre 2009) : 201–10. http://dx.doi.org/10.1017/s1743921310004138.

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AbstractThe nuclei of the lithium isotopes are fragile, easily destroyed, so that, at variance with most of the other elements, they cannot be formed in stars through steady hydrostatic nucleosynthesis.The 7Li isotope is synthesized during primordial nucleosynthesis in the first minutes after the Big Bang and later by cosmic rays, by novae and in pulsations of AGB stars (possibly also by the ν process). 6Li is mainly formed by cosmic rays. The oldest (most metal-deficient) warm galactic stars should retain the signature of these processes if, (as it had been often expected) lithium is not depleted in these stars. The existence of a “plateau” of the abundance of 7Li (and of its slope) in the warm metal-poor stars is discussed. At very low metallicity ([Fe/H] < −2.7dex) the star to star scatter increases significantly towards low Li abundances. The highest value of the lithium abundance in the early stellar matter of the Galaxy (logϵ(Li) = A(7Li) = 2.2 dex) is much lower than the the value (logϵ(Li) = 2.72) predicted by the standard Big Bang nucleosynthesis, according to the specifications found by the satellite WMAP. After gathering a homogeneous stellar sample, and analysing its behaviour, possible explanations of the disagreement between Big Bang and stellar abundances are discussed (including early astration and diffusion). On the other hand, possibilities of lower productions of 7Li in the standard and/or non-standard Big Bang nucleosyntheses are briefly evoked.A surprisingly high value (A(6Li)=0.8 dex) of the abundance of the 6Li isotope has been found in a few warm metal-poor stars. Such a high abundance of 6Li independent of the mean metallicity in the early Galaxy cannot be easily explained. But are we really observing 6Li?
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Sneden, Christopher, James E. Lawler, Elizabeth A. Den Hartog et Michael E. Wood. « Atomic Data for Stellar Nucleosynthesis ». Proceedings of the International Astronomical Union 11, A29A (août 2015) : 287–90. http://dx.doi.org/10.1017/s1743921316003069.

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AbstractStellar chemical composition analyses can only yield reliable abundances if the atomic transition parameters are accurately determined. During the last couple of decades a renewed emphasis on laboratory spectroscopy has produced large sets of useful atomic transition probabilities for species of interest to stellar spectroscopists. In many cases the transition data are of such high quality that they play little part in the abundance uncertainties. We summarize the current state of atomic parameters, highlighting the areas of satisfactory progress and noting places, where further laboratory progress will be welcome.
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Cristallo, Sergio. « Neutron captures in stellar nucleosynthesis ». EPJ Web of Conferences 275 (2023) : 01006. http://dx.doi.org/10.1051/epjconf/202327501006.

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Apart from cosmological hydrogen and helium, chemical elements in the Universe are produced in stars, during both quiescent and explosive phases. The Sun chemical distribution witnesses the pollution from already extinct stellar generations at different epochs before the Solar System formation. The two major nucleosynthesis processes responsible for the formation of elements heavier than iron are the slow neutron capture process (the s-process) and the rapid neutron capture process (the r-process). A third, less common, nucleosynthesis channel is related to the intermediate neutron capture process (the i-process), whose existence is not ascertained yet. Finally, a few proton-rich isotopes are created by the p-process. I will show their characteristics and the stellar sites where they are at work.
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Karakas, Amanda I. « Stellar yields – theory and observations ». Proceedings of the International Astronomical Union 11, A29B (août 2015) : 162–63. http://dx.doi.org/10.1017/s1743921316004713.

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AbstractStellar yields are an essential tool for studies of chemical evolution. For low and intermediate-mass stars (0.8 up to 8-10M⊙) the richest nucleosynthesis occurs when the stars are on the asymptotic giant branch (AGB) of stellar evolution. We discuss the main nucleosynthesis outcomes, along with the uncertainties that affect the theoretical calculations. The uncertainties in the physics can be improved by comparing theoretical models to observations, including chemically peculiar metal-poor stars, along with AGB stars and their progeny.
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Hollowell, David, et Icko Iben. « Nucleosynthesis and Mixing in Low- and Intermediate-Mass AGB Stars ». International Astronomical Union Colloquium 108 (1988) : 38–43. http://dx.doi.org/10.1017/s0252921100093374.

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AbstractThe existence of carbon stars brighter than Mbol=-4 can be understood in terms of dredge up in thermally pulsing asymptotic giant branch (AGB) stars. As a low- or intermediate-mass star evolves on the AGB, the large fluxes engendered in a helium shell flash cause the base of the convective envelope to extend into the radiative, carbon-rich region, and transport nucleosynthesis products to the stellar surface. Numerical models indicate that AGB stars with sufficiently massive stellar envelopes can become carbon stars via this standard dredge-up mechanism. AGB stars with less massive stellar envelopes can become carbon stars when carbon recombines in the cool, carbon-rich region below the convective envelope.Neutron capture occurs on iron-seed nuclei during a shell flash, and the products of this nucleosynthesis are also carried to the stellar surface. The conversion of 22Ne into 25Mg can initiate neutron capture nucleosynthesis in largecore mass AGB stars, but only if these stars can survive their large mass loss rates. The current estimates of nuclear reaction rates do not allow for appreciable neutron capture nucleosynthesis via the 22Ne source in lower mass AGB stars. The carbon recombination that induces dredge up in AGB stars of small envelope mass, however, also induces mixing of 1H and 12C in such a way that ultimately a 13C neutron source is activated in these stars. The 13C source can provide an abundant supply of neutrons for the nucleosynthesis of both light and heavy elements. While the existence of neutron-nucleosynthesis products in AGB stellar atmospheres can be understood qualitatively in terms of an active neutron source, the combination of nuclear reaction theory and evolutionary models has yet to provide quantitative agreement with stellar observations.
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Woosley, S. E., A. Heger, L. Roberts et R. D. Hoffman. « Nucleosynthesis Now and Then ». Proceedings of the International Astronomical Union 5, S265 (août 2009) : 3–11. http://dx.doi.org/10.1017/s1743921310000086.

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AbstractToday we understand, to reasonable accuracy, the origin of most of the abundant elements in the sun and similar Population I stars. Given our relatively primitive ability to model supernova explosion mechanisms, stellar mass loss, and stellar mixing, this is a remarkable achievement. This understanding is possible, in part, because supernovae are highly constrained by their spectra, light curves and the sorts of remnants they leave. This same understanding extends to the major abundances seen in primitive metal-poor stars down to [Fe/H] > −4. In particular, one finds no compelling evidence for exotic energies or unusual stellar properties. There are exceptions, however. About half of the isotopes above iron, ther-process and thep-process withA< 130, still have an uncertain origin, both in the sun and in metal-poor stars. The abundances in the hyper-iron-poor stars ([Fe/H] < −4) also require a special explanation. We suggest that they represent the operation of a first generation of massive stars that produced almost exclusively C, N, and O and black holes, a generation in which 100 M⊙were abundant, but stars over about 150 M⊙and under 30 M⊙were almost absent.
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Cahoone, Lawrence E. « Is Stellar Nucleosynthesis a Good Thing ? » Environmental Ethics 38, no 4 (2016) : 421–39. http://dx.doi.org/10.5840/enviroethics201638436.

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Stasińska, G. « Planetary Nebulae, Tracers of Stellar Nucleosynthesis ». EAS Publications Series 32 (2008) : 173–85. http://dx.doi.org/10.1051/eas:0832005.

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Gustafsson, B. « Nucleosynthesis and future stellar abundance determinations ». EAS Publications Series 11 (2004) : 21–50. http://dx.doi.org/10.1051/eas:2004002.

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Käppeler, F. « Reaction rates, nucleosynthesis, and stellar structure ». Nuclear Instruments and Methods in Physics Research Section B : Beam Interactions with Materials and Atoms 259, no 1 (juin 2007) : 663–68. http://dx.doi.org/10.1016/j.nimb.2007.01.296.

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Schatz, Gerd. « The s-process of stellar nucleosynthesis ». Progress in Particle and Nuclear Physics 17 (janvier 1986) : 393–417. http://dx.doi.org/10.1016/0146-6410(86)90027-x.

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Wannier, Peter G. « Abundances in the Galactic Center ». Symposium - International Astronomical Union 136 (1989) : 107–19. http://dx.doi.org/10.1017/s0074180900186395.

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Abundance measurements in the Galactic Center (GC) probe material with a nucleosynthetic history unique in our Galaxy. The measurements are of two types: probing interstellar and stellar material. Measurements of gas-phase abundances are mostly toward SgrB2 and SgrA. They reflect the current state of nuclear evolution in the GC and include several important isotope abundance ratios. The isotope ratios provide the most accurate information and allow for comparison with results elsewhere in the interstellar medium. The second type of measurement is of abundances in (and around) stars, yielding chemical abundances in the bulge and disc populations, and reflecting the state of nuclear evolution when the stars were born.When combined with our knowledge of evolution in the solar neighborhood, several of the results are consistent with the the greater nuclear “maturity” of the inner Galaxy. However, there are several important exceptions, which point to the fact that we really do not understand nuclear processing in the GC region. Some of the open issues may be resolved observationally, and with new infrared and millimeterwave techniques a clear opportunity exists to improve the observational record. Results should increase our understanding of stellar nucleosynthesis and of the history of star formation in the GC.
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Sergi, Maria Letizia, Giuseppe D’Agata, Giovanni Luca Guardo, Giuseppe Gabriele Rapisarda, Vaclav Burjan, Silvio Cherubini, Marisa Gulino et al. « Trojan Horse Investigation for AGB Stellar Nucleosynthesis ». Universe 8, no 2 (16 février 2022) : 128. http://dx.doi.org/10.3390/universe8020128.

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Asymptotic Giant Branch (AGB) stars are among the most important astrophysical sites influencing the nucleosynthesis and the chemical abundances in the Universe. From a pure nuclear point of view, several processes take part during this peculiar stage of stellar evolution thus requiring detailed experimental cross section measurements. Here, we report on the most recent results achieved via the application of the Trojan Horse Method (THM) and Asymptotic Normalization Coefficient (ANC) indirect techniques, discussing the details of the experimental procedure and the deduced reaction rates. In addition, we report also on the on going studies of interest for AGB nucleosynthesis.
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Schramm, D. N. « Big Bang Nucleosynthesis ». Symposium - International Astronomical Union 187 (2002) : 1–15. http://dx.doi.org/10.1017/s0074180900113695.

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Big Bang Nucleosynthesis (BBN) is on the verge of undergoing a transformation now that extragalactic deuterium is being measured. Previously, the emphasis was on demonstrating the concordance of the Big Bang Nucleosynthesis model with the abundances of the light isotopes extrapolated back to their primordial values using stellar and Galactic evolution theories. Once the primordial deuterium abundance is converged upon, the nature of the field will shift to using the much more precise primordial D/H to constrain the more flexible stellar and Galactic evolution models (although the question of potential systematic error in 4He abundance determinations remains open). The remarkable success of the theory to date in establishing the concordance has led to the very robust conclusion of BBN regarding the baryon density. The BBN constraints on the cosmological baryon density are reviewed and demonstrate that the bulk of the baryons are dark and also that the bulk of the matter in the universe is non-baryonic. Comparison of baryonic density arguments from Lyman-α clouds, x-ray gas in clusters, the Sunyaev-Zeldovich effect, and the microwave anisotropy are made and shown to be consistent with the BBN value.
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de los Reyes, Mithi A. C., Evan N. Kirby, Alexander P. Ji et Evan H. Nuñez. « Simultaneous Constraints on the Star Formation History and Nucleosynthesis of Sculptor dSph ». Astrophysical Journal 925, no 1 (1 janvier 2022) : 66. http://dx.doi.org/10.3847/1538-4357/ac332b.

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Abstract We demonstrate that using up to seven stellar abundance ratios can place observational constraints on the star formation histories (SFHs) of Local Group dSphs, using Sculptor dSph as a test case. We use a one-zone chemical evolution model to fit the overall abundance patterns of α elements (which probe the core-collapse supernovae that occur shortly after star formation), s-process elements (which probe AGB nucleosynthesis at intermediate delay times), and iron-peak elements (which probe delayed Type Ia supernovae). Our best-fit model indicates that Sculptor dSph has an ancient SFH, consistent with previous estimates from deep photometry. However, we derive a total star formation duration of ∼0.9 Gyr, which is shorter than photometrically derived SFHs. We explore the effect of various model assumptions on our measurement and find that modifications to these assumptions still produce relatively short SFHs of duration ≲1.4 Gyr. Our model is also able to compare sets of predicted nucleosynthetic yields for supernovae and AGB stars, and can provide insight into the nucleosynthesis of individual elements in Sculptor dSph. We find that observed [Mn/Fe] and [Ni/Fe] trends are most consistent with sub-M Ch Type Ia supernova models, and that a combination of “prompt” (delay times similar to core-collapse supernovae) and “delayed” (minimum delay times ≳50 Myr) r-process events may be required to reproduce observed [Ba/Mg] and [Eu/Mg] trends.
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Weiss, Achim. « Round table discussion on session D : stellar evolution, nucleosynthesis and convective mixing ». Proceedings of the International Astronomical Union 2, S239 (août 2006) : 294–95. http://dx.doi.org/10.1017/s1743921307000579.

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Meynet, Georges. « Rotation, mass loss and nucleosynthesis ». Proceedings of the International Astronomical Union 2, no 14 (août 2006) : 209. http://dx.doi.org/10.1017/s1743921307010216.

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Giannaka, P. G., et T. S. Kosmas. « Electron Capture Cross Sections for Stellar Nucleosynthesis ». Advances in High Energy Physics 2015 (2015) : 1–11. http://dx.doi.org/10.1155/2015/398796.

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In the first stage of this work, we perform detailed calculations for the cross sections of the electron capture on nuclei under laboratory conditions. Towards this aim we exploit the advantages of a refined version of the proton-neutron quasiparticle random-phase approximation (pn-QRPA) and carry out state-by-state evaluations of the rates of exclusive processes that lead to any of the accessible transitions within the chosen model space. In the second stage of our present study, we translate the abovementionede--capture cross sections to the stellar environment ones by inserting the temperature dependence through a Maxwell-Boltzmann distribution describing the stellar electron gas. As a concrete nuclear target we use the66Zn isotope, which belongs to the iron group nuclei and plays prominent role in stellar nucleosynthesis at core collapse supernovae environment.
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Chiosi, C. « Stellar Nucleosynthesis and Chemical Evolution of Galaxies ». EAS Publications Series 27 (2007) : 25–39. http://dx.doi.org/10.1051/eas:2007142.

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Schuler, Simon C., Jeremy R. King et Lih-Sin The. « STELLAR NUCLEOSYNTHESIS IN THE HYADES OPEN CLUSTER ». Astrophysical Journal 701, no 1 (27 juillet 2009) : 837–49. http://dx.doi.org/10.1088/0004-637x/701/1/837.

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33

Reifarth, René, Stefan Fiebiger, Kathrin Göbel, Tanja Heftrich, Tanja Kausch, Christoph Köppchen, Deniz Kurtulgil, Christoph Langer, Benedikt Thomas et Mario Weigand. « Treatment of isomers in nucleosynthesis codes ». International Journal of Modern Physics A 33, no 09 (30 mars 2018) : 1843011. http://dx.doi.org/10.1142/s0217751x1843011x.

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The decay properties of long-lived excited states (isomers) can have a significant impact on the destruction channels of isotopes under stellar conditions. In sufficiently hot environments, the population of isomers can be altered via thermal excitation or de-excitation. If the corresponding lifetimes are of the same order of magnitude as the typical time scales of the environment, the isomers have to be treated explicitly. We present a general approach to the treatment of isomers in stellar nucleosynthesis codes and discuss a few illustrative examples. The corresponding code is available online at http://exp-astro.de/isomers/ .
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34

Shetye, S., S. Goriely, L. Siess, S. Van Eck, A. Jorissen et H. Van Winckel. « Observational evidence of third dredge-up occurrence in S-type stars with initial masses around 1 M⊙ ». Astronomy & ; Astrophysics 625 (30 avril 2019) : L1. http://dx.doi.org/10.1051/0004-6361/201935296.

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Context. S stars are late-type giants with spectra showing characteristic molecular bands of ZrO in addition to the TiO bands typical of M stars. Their overabundance pattern shows the signature of s-process nucleosynthesis. Intrinsic, technetium (Tc)-rich S stars are the first objects on the asymptotic giant branch (AGB) to undergo third dredge-up (TDU) events. Exquisite Gaia parallaxes now allow for these stars to be precisely located in the Hertzsprung–Russell (HR) diagram. Here we report on a population of low-mass, Tc-rich S stars previously unaccounted for by stellar evolution models. Aims. Our aim is to derive parameters for a sample of low-mass, Tc-rich S stars and then, by comparing their location in the HR diagram with stellar evolution tracks, to derive their masses and to compare their measured s-process abundance profiles with recently derived STAREVOL nucleosynthetic predictions for low-mass AGB stars. Methods. Stellar parameters were obtained using a combination of HERMES high-resolution spectra, accurate Gaia Data Release 2 (Gaia-DR2) parallaxes, stellar-evolution models, and newly designed MARCS model atmospheres for S-type stars. Results. We report on six Tc-rich S stars lying close to the 1 M⊙ (initial mass) tracks of AGB stars of the corresponding metallicity and above the predicted onset of TDU, as expected. This provides direct evidence for TDUs occurring in AGB stars with initial masses as low as ∼1 M⊙ and at low luminosity, that is, at the start of the thermally pulsing AGB. We present AGB models producing TDU in those stars with [Fe/H] in the range −0.25 to −0.5. There is reasonable agreement between the measured and predicted s-process abundance profiles. For two objects however, CD −29°5912 and BD +34°1698, the predicted C/O ratio and s-process enhancements do not simultaneously match the measured ones.
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35

Matteucci, F. « The Galactic Chemical Evolution of Lithium ». Highlights of Astronomy 10 (1995) : 457. http://dx.doi.org/10.1017/s1539299600011734.

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Under the assumption that the abundance of 7Li in Population II stars represents the primordial Li abundance (with perhaps a small contribution from GCR spallation) and that GCR spallation/fusion processes cannot contribute to more than ≃ 10 − 20% of the Li abundance observed in Pop. I stars and in the solar system, one must conclude that most of Li in Pop. I stars has a stellar origin.Possible stellar Li producers are discussed: low mass AGB stars (2−5M⊙) (C-stars), high mass AGB stars (5 - 8M⊙), supernovae of type II (M > 10M⊙) and novae. The various problems connected with all of these sources are indicated: in particular, we discuss the Li production in AGB stars when evolutionary effects due to the metallicity are taken into account, and the fact that novae do not seem to be good candidate for Li production, as suggested by a recent nucleosynthesis study. We then calculate the yields from these stellar sources and predict the behavior of log N(Li) vs. [Fe/H] by means of a galactic chemical evolution model.We conclude that, although a unique model cannot be found, due to the uncertainties still existing in the stellar nucleosynthesis, the most likely scenario is that Li is partly produced in type II supernovae (v-induced nucleosynthesis) and partly in massive AGB stars.
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36

Gustafsson, Bengt, et Nils Ryde. « Carbon Stars and Nucleosynthesis in Galaxies ». Symposium - International Astronomical Union 177 (2000) : 481–96. http://dx.doi.org/10.1017/s007418090000276x.

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The role of carbon stars in the build-up of chemical elements in galaxies is discussed on the basis of stellar evolution calculations and estimated stellar yields, abundance analyses of AGB stars, galactic-evolution models and abundance trends among solar-type disk stars. We conclude that the AGB stars in general, and carbon stars in particular, probably are main contributors of s-elements, that their contributions of flourine and carbon are quite significant, and that possibly their contributions of lithium, 13C and 22Ne are of some importance. Also contributions of N, Na and Al are discussed. The major uncertainties that characterize almost any statement concerning these issues are underlined.
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Izzard, Robert G., et Christopher A. Tout. « Nucleosynthesis in Binary Populations ». Publications of the Astronomical Society of Australia 20, no 4 (2003) : 345–50. http://dx.doi.org/10.1071/as03026.

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AbstractWe investigate the effect of duplicity on stellar yields of carbon, nitrogen, and oxygen. Populations of single and binary stars are modelled and the yields calculated for the whole population. The effects of explosive nucleosynthesis in novae and supernovae are included but by artificially removing these effects from our populations we determine the influence of a binary companion on asymptotic giant branch yields of the CNO elements.
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38

Truran, James W. « Chemical Evolution of Galaxies : Abundance Trends and Implications ». Symposium - International Astronomical Union 145 (1991) : 13–19. http://dx.doi.org/10.1017/s0074180900227228.

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Recent spectroscopic studies of the elemental abundance patterns associated with extremely metal deficient field halo stars and globular cluster stars are briefly reviewed. These metal deficient stellar populations have been found to be characterized by abundance patterns which differ quite distinctly from those of solar system abundances, but are consistent with the view that they reflect primarily the nucleosynthesis products of the evolution of massive stars and associated Type II supernovae. Guided by our current knowledge of nucleosynthesis as a function of stellar mass occurring in stars and supernovae, we identify some interesting constraints upon theories of the formation and early history of our Galaxy.
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39

Traat, Peeter. « Metallicity-dependent Spectral Evolution ». Symposium - International Astronomical Union 192 (1999) : 377–80. http://dx.doi.org/10.1017/s0074180900204397.

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The initial chemical composition of stars is, besides the mass, another key factor in stellar evolution. Through stellar lifetimes and impact on radiation output and nucleosynthesis of stars it is controlling both the pace of evolution of galactic matter/light and changes in their integrated observables and spectra.
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40

Akram, Waheed, Oliver Hallmann, Bernd Pfeiffer et Karl-Ludwig Kratz. « On the Nucleosynthetic Origin of Presolar Silicon Carbide X-Grains ». Universe 8, no 12 (28 novembre 2022) : 629. http://dx.doi.org/10.3390/universe8120629.

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In this paper we present an extension of our nucleosynthesis parameter study within the classical neutrino-driven wind scenario of core-collapse supernovae (ccSNe). The principal aim of this decade-old study was to shine light on the production of the historical ‘p-only’ isotopes of the light trans-Fe elements in the Solar System (S.S.). One of our earliest key findings was the co-production of neighbouring classical ‘s-only’ and ‘r-only’ isotopes between Zn (Z = 30) and Ru (Z = 44), alongside the synthesis of light p-isotopes, under similar conditions of a moderately neutron-rich, low-entropy, charged-particle component of Type II SNe wind ejecta. We begin this analysis by expressing the need for nuclear-structure input from detailed spectroscopic experiments and microscopic models in the relevant shape-transition mass region between N = 50 and N = 60. Then, we focus on the unique nucleosynthetic origin of the anomalous isotopic compositions of Zr (Z = 40), Mo (Z = 42) and Ru (Z = 44) in presolar silicon carbide X-grains. In contrast to the interpretation of other studies, we show that these grains do not reflect the signature of a ‘clean’ stellar scenario but are mixtures of an exotic rapid (r-process like) nucleosynthesis component and different fractions of S.S. material. Thus, the synthesis of these light isotopes through a ‘primary’ production mode provides further means to revise the abundance estimates of the light trans-Fe elements in the S.S., reducing our dependence on still favoured ‘secondary’ scenarios like Type Ia SNe or neutron-bursts in exploding massive stars.
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41

Van Eck, Sophie, Shreeya Shetye et Lionel Siess. « Insights into AGB Nucleosynthesis Thanks to Spectroscopic Abundance Measurements in Intrinsic and Extrinsic Stars ». Universe 8, no 4 (29 mars 2022) : 220. http://dx.doi.org/10.3390/universe8040220.

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The foundations of stellar nucleosynthesis have been established more than 70 years ago. Since then, much progress has been made, both on the theoretical side, with stellar evolution and nucleosynthesis models of increasing complexity, using more and more accurate nuclear data, and on the observational side, with the number of analyzed stars growing tremendously. In between, the complex machinery of abundance determination has been refined, taking into account model atmospheres of non-solar chemical composition, three-dimensional, non-LTE (non-local thermodynamic equilibrium) effects, and a growing number of atomic and molecular data. Neutron-capture nucleosynthesis processes, and in particular the s-process, have been scrutinized in various types of evolved stars, among which asymptotic giant branch stars, carbon-enhanced metal-poor stars and post-AGB stars. We review here some of the successes of the comparison between models and abundance measurements of heavy elements in stars, including in binaries, and outline some remaining unexplained features.
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42

Battino, Umberto, Marco Pignatari, Ashley Tattersall, Pavel Denissenkov et Falk Herwig. « The NuGrid AGB Evolution and Nucleosynthesis Data Set ». Universe 8, no 3 (9 mars 2022) : 170. http://dx.doi.org/10.3390/universe8030170.

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Asymptotic Giant Branch (AGB) stars play a key role in the chemical evolution of galaxies. These stars are the fundamental stellar site for the production of light elements such as C, N and F, and half of the elements heavier than Fe via the slow neutron capture process (s-process). Hence, detailed computational models of AGB stars’ evolution and nucleosynthesis are essential for galactic chemical evolution. In this work, we discuss the progress in updating the NuGrid data set of AGB stellar models and abundance yields. All stellar models have been computed using the MESA stellar evolution code, coupled with the post-processing mppnp code to calculate the full nucleosynthesis. The final data set will include the initial masses Mini/M⊙ = 1, 1.65, 2, 3, 4, 5, 6 and 7 for initial metallicities Z = 0.0001, 0.001, 0.006, 0.01, 0.02 and 0.03. Observed s-process abundances on the surfaces of evolved stars as well as the typical light elements in the composition of H-deficient post-AGB stars are reproduced. A key short-term goal is to complete and expand the AGB stars data set for the full metallicity range. Chemical yield tables are provided for the available models.
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43

El Eid, Mounib F. « Heavy Element Nucleosynthesis ». EPJ Web of Conferences 184 (2018) : 01007. http://dx.doi.org/10.1051/epjconf/201818401007.

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This contribution deals with the important subject of the nucleosynthesis of heavy elements in the Galaxy. After an overview of several observational features, the physical processes responsible mainly for the formation of heavy elements will be described and linked to possible stellar sites and to galactic chemical evolution. In particular, we focus on the neutron-capture processes, namely the s-process (slow neutron capture) and the r-process (rapid neutron capture) and discuss some problems in connection with their sites and their outcome. The aim is to give a brief overview on the exciting subject of the heavy element nucleosynthesis in the Galaxy, emphasizing its importance to trace the galactic chemical evolution and illustrating the challenge of this subject.
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44

Hashimoto, M., K. Nomoto, T. Tsujimoto et F. K. Thielemann. « Supernova Nucleosynthesis in Massive Stars ». International Astronomical Union Colloquium 145 (1996) : 157–64. http://dx.doi.org/10.1017/s0252921100008022.

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Presupernova evolution and explosive nucleosynthesis in massive stars for main-sequence masses from 13 Mʘ to 70 Mʘ are calculated. We examine the dependence of the supernova yields on the stellar mass, 12C(α, γ)16O rate, and explosion energy. The supernova yields integrated over the initial mass function are compared with the solar abundances.
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45

Nomoto, K., N. Tominaga, M. Tanaka, K. Maeda et H. Umeda. « The Connection between Gamma-Ray Bursts and Extremely Metal-Poor Stars as Nucleosynthetic Probes of the Early Universe ». Proceedings of the International Astronomical Union 3, S250 (décembre 2007) : 463–70. http://dx.doi.org/10.1017/s1743921308020838.

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AbstractThe connection between the long GRBs and Type Ic Supernovae (SNe) has revealed the interesting diversity: (i) GRB-SNe, (ii) Non-GRB Hypernovae (HNe), (iii) X-Ray Flash (XRF)-SNe, and (iv) Non-SN GRBs (or dark HNe). We show that nucleosynthetic properties found in the above diversity are connected to the variation of the abundance patterns of extremely-metal-poor (EMP) stars, such as the excess of C, Co, Zn relative to Fe. We explain such a connection in a unified manner as nucleosynthesis of hyper-aspherical (jet-induced) explosions of Pop III core-collapse SNe. We show that (1) the explosions with large energy deposition rate, Ėdep, are observed as GRB-HNe and their yields can explain the abundances of normal EMP stars, and (2) the explosions with small Ėdepare observed as GRBs without bright SNe and can be responsible for the formation of the C-rich EMP (CEMP) and the hyper metal-poor (HMP) stars. We thus propose that GRB-HNe and the Non-SN GRBs (dark HNe) belong to a continuous series of BH-forming massive stellar deaths with the relativistic jets of different Ėdep.
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46

Smith, Verne V. « Stellar Metallicities in the Magellanic Clouds ». Symposium - International Astronomical Union 190 (1999) : 259–65. http://dx.doi.org/10.1017/s0074180900118005.

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The overall stellar metallicity scale as a function of age for both Magellanic Clouds reveals that they have followed a different pattern of enrichment when compared to each other as well as to the Galactic disk. In addition, an investigation into the abundances of two key elements, oxygen and europium, shows that the detailed nucleosynthesis history of these systems is unique in comparison to any Galactic population yet studied.
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47

Palmerini, S., G. D’Agata, M. La Cognata, R. G. Pizzone, I. Indelicato, O. Trippella et D. Vescovi. « On the fluorine nucleosynthesis in AGB stars in the light of the 19F(p,α)16O and 19F(α,p)22Ne reaction rate measured via THM ». International Journal of Modern Physics : Conference Series 49 (janvier 2019) : 1960011. http://dx.doi.org/10.1142/s2010194519600115.

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In the last years the [Formula: see text]O and the [Formula: see text]F([Formula: see text],p)[Formula: see text]Ne reactions have been studied via the Trojan Horse Method in the energy range of interest for astrophysics. These are the first experimental data available for the main channels of [Formula: see text]F destruction that entirely cover the energy regions typical of the stellar H- and He- burning. In both cases the reaction rates are significantly larger than the previous estimations available in the literature. We present here a re-analysis of the fluorine nucleosynthesis in Asymptotic Giant Branch stars by employing in state-of-the-art models of stellar nucleosynthesis the THM reaction rates for [Formula: see text]F destruction.
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48

Giovagnoli, A., et M. Tosi. « Chemical evolution models with a new stellar nucleosynthesis ». Monthly Notices of the Royal Astronomical Society 273, no 2 (15 mars 1995) : 499–504. http://dx.doi.org/10.1093/mnras/273.2.499.

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49

Levi, Barbara Goss. « New Data Strengthen Weak Link in Stellar Nucleosynthesis ». Physics Today 46, no 7 (juillet 1993) : 23–25. http://dx.doi.org/10.1063/1.2808959.

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Thielemann, F. K., D. Argast, F. Brachwitz, W. R. Hix, P. Höflich, M. Liebendörfer, G. Martinez-Pinedo, A. Mezzacappa, I. Panov et T. Rauscher. « Nuclear cross sections, nuclear structure and stellar nucleosynthesis ». Nuclear Physics A 718 (mai 2003) : 139–46. http://dx.doi.org/10.1016/s0375-9474(03)00704-8.

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