68 results on '"Sara Bisterzo"'
Search Results
2. Simultaneous iron and nickel isotopic analyses of presolar silicon carbide grains
- Author
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Thomas Stephan, Reto Trappitsch, Roberto Gallino, Frank Gyngard, Andrew M. Davis, Sergio Cristallo, Detlef Rost, Michael R. Savina, Michael J. Pellin, Sara Bisterzo, Nicolas Dauphas, ITA, and USA
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Silicon ,Presolar grains ,Radiochemistry ,Analytical chemistry ,chemistry.chemical_element ,010502 geochemistry & geophysics ,01 natural sciences ,Nickel ,Stellar nucleosynthesis ,chemistry ,Geochemistry and Petrology ,Nucleosynthesis ,0103 physical sciences ,Asymptotic giant branch ,Nuclide ,s-process ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
Aside from recording stellar nucleosynthesis, a few elements in presolar grains can also provide insights into the galactic chemical evolution (GCE) of nuclides. We have studied the carbon, silicon, iron, and nickel isotopic compositions of presolar silicon carbide (SiC) grains from asymptotic giant branch (AGB) stars to better understand GCE. Since only the neutron-rich nuclides in these grains have been heavily influenced by the parent star, the neutron-poor nuclides serve as GCE proxies. Using CHILI, a new resonance ionization mass spectrometry (RIMS) instrument, we measured 74 presolar SiC grains for all iron and nickel isotopes. With the CHARISMA instrument, 13 presolar SiC grains were analyzed for iron isotopes. All grains were also measured by NanoSIMS for their carbon and silicon isotopic compositions. A comparison of the measured neutron-rich isotopes with models for AGB star nucleosynthesis shows that our measurements are consistent with AGB star predictions for low-mass stars between half-solar and solar metallicity. Furthermore, our measurements give an indication on the 22 Ne ( α ,n ) 25 Mg reaction rate. In terms of GCE, we find that the GCE-dominated iron and nickel isotope ratios, 54 Fe / 56 Fe and 60 Ni / 58 Ni , correlate with their GCE-dominated counterpart in silicon, 29 Si / 28 Si . The measured GCE trends include the Solar System composition, showing that the Solar System is not a special case. However, as seen in silicon and titanium, many presolar SiC grains are more evolved for iron and nickel than the Solar System. This confirms prior findings and agrees with observations of large stellar samples that a simple age-metallicity relationship for GCE cannot explain the composition of the solar neighborhood.
- Published
- 2018
3. Observing the metal-poor solar neighbourhood: a comparison of galactic chemical evolution predictions*†
- Author
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N. Basak, Claudia Travaglio, Benoit Côté, V. V. Kovtyukh, Caroline Soubiran, C. J. Jordan, Brad K. Gibson, S. A. Korotin, Marco Pignatari, Sara Bisterzo, Benjamin Wehmeyer, Friedrich-Karl Thielemann, Adam Paul, C. Ritter, Falk Herwig, T. V. Mishenina, T. I. Gorbaneva, Astronomical observatory of Odessa National University [Odessa], Odessa National I.I.Mechnikov University, M2A 2017, Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Unité de recherche Géochimie des Sols et des Eaux (URGSE), Institut National de la Recherche Agronomique (INRA), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Collège de France (CdF (institution))-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut National de la Recherche Agronomique (INRA), Helmholtz Centre for Infection Research (HZI), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Collège de France (CdF)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Institut National de la Recherche Agronomique (INRA), and Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Physics ,010308 nuclear & particles physics ,Thermodynamic equilibrium ,Neighbourhood (graph theory) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,Spectral line ,[SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM] ,Metal ,Stars ,Supernova ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,visual_art ,0103 physical sciences ,Galaxy formation and evolution ,visual_art.visual_art_medium ,Dispersion (chemistry) ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
Atmospheric parameters and chemical compositions for ten stars with metallicities in the region of -2.2< [Fe/H], Comment: 25 pages, 7 figures
- Published
- 2017
4. Enrichment of the Galactic disc with neutron capture elements: Sr
- Author
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Sara Bisterzo, Claudia Travaglio, Caroline Soubiran, Marco Pignatari, T. V. Mishenina, Friedrich-Karl Thielemann, T. I. Gorbaneva, Astronomical observatory of Odessa National University [Odessa], Odessa National I.I.Mechnikov University, M2A 2019, Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), and Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
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Physics ,010308 nuclear & particles physics ,Metallicity ,Milky Way ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,[SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM] ,Stars ,Stellar nucleosynthesis ,Space and Planetary Science ,Nucleosynthesis ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Galaxy formation and evolution ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
The enrichment history of heavy neutron-capture elements in the Milky Way disc provides fundamental information about the chemical evolution of our Galaxy and about the stellar sources that made those elements. In this work we give new observational data for Sr, the element at the first neutron-shell closure beyond iron, N=50, based on the analysis of the high resolution spectra of 276 Galactic disc stars. The Sr abundance was derived by comparing the observed and synthetic spectra in the region of the SrI 4607 A line, making use of the LTE approximation. NLTE corrections lead to an increase of the abundance estimates obtained under LTE, but for these lines they are minor near solar metallicity. The average correction that we find is 0.151 dex. The star that is mostly affected is HD 6582, with a 0.244 dex correction. The behavior of the Sr abundance as a function of metallicity is discussed within a stellar nucleosynthesis context, in comparison with the abundance of the heavy neutron-capture elements Ba (Z=56) and Eu (Z=63). The comparison of the observational data with the current GCE models confirm that the s-process contributions from Asymptotic Giant Branch stars and from massive stars are the main sources of Sr in the Galactic disc and in the Sun, while different nucleosynthesis sources can explain the high [Sr/Ba] and [Sr/Eu] ratios observed in the early Galaxy., 16 pages, 14 figures, accepted for publication in MNRAS
- Published
- 2019
5. Mass and metallicity requirement in stellar models for galactic chemical evolution applications
- Author
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Alexander Heger, Claudia Travaglio, Brian W. O'Shea, Sara Bisterzo, Falk Herwig, Christian Ritter, Benoit Côté, and Christopher West
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Physics ,Milky Way ,Metallicity ,FOS: Physical sciences ,Astronomy ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,Chemical evolution ,Stars ,Supernova ,13. Climate action ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Galaxy formation and evolution ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,010306 general physics ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
We used a one-zone chemical evolution model to address the question of how many masses and metallicities are required in grids of massive stellar models in order to ensure reliable galactic chemical evolution predictions. We used a set of yields that includes seven masses between 13 and 30 Msun, 15 metallicities between 0 and 0.03 in mass fraction, and two different remnant mass prescriptions. We ran several simulations where we sampled subsets of stellar models to explore the impact of different grid resolutions. Stellar yields from low- and intermediate-mass stars and from Type Ia supernovae have been included in our simulations, but with a fixed grid resolution. We compared our results with the stellar abundances observed in the Milky Way for O, Na, Mg, Si, Ca, Ti, and Mn. Our results suggest that the range of metallicity considered is more important than the number of metallicities within that range, which only affects our numerical predictions by about 0.1 dex. We found that our predictions at [Fe/H] < -2 are very sensitive to the metallicity range and the mass sampling used for the lowest metallicity included in the set of yields. Variations between results can be as high as 0.8 dex, for any remnant mass prescription. At higher [Fe/H], we found that the required number of masses depends on the element of interest and on the remnant mass prescription. With a monotonic remnant mass prescription where every model explodes as a core-collapse supernova, the mass resolution induces variations of 0.2 dex on average. But with a remnant mass prescription that includes islands of non-explodability, the mass resolution can cause variations of about 0.2 to 0.7 dex depending on the choice of metallicity range. With such a prescription, explosive or non-explosive models can be missed if not enough masses are selected, resulting in over- or under-estimations of the mass ejected by massive stars., 14 pages, 2 tables, 14 figures, submitted to MNRAS
- Published
- 2016
6. New constraints on the major neutron source in low-mass AGB stars
- Author
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Reto Trappitsch, Sergio Cristallo, Andrew M. Davis, Larry R. Nittler, Sara Bisterzo, Roberto Gallino, Nan Liu, ITA, and USA
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Physics ,Nuclear reaction ,Meteoroid ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Stars ,Meteorite ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Nucleosynthesis ,0103 physical sciences ,Asymptotic giant branch ,Neutron source ,010306 general physics ,Low Mass ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
We compare updated Torino postprocessing asymptotic giant branch (AGB) nucleosynthesis model calculations with isotopic compositions of mainstream SiC dust grains from low-mass AGB stars. Based on the data-model comparison, we provide new constraints on the major neutron source, 13C({\alpha},n)16O in the He-intershell, for the s-process. We show that the literature Ni, Sr, and Ba grain data can only be consistently explained by the Torino model calculations that adopt the recently proposed magnetic-buoyancy-induced 13C-pocket. This observation provides strong support to the suggestion of deep mixing of H into the He-intershell at low 13C concentrations as a result of efficient transport of H through magnetic tubes., Comment: ApJ, accepted
- Published
- 2018
7. Stellar Parameters, Chemical composition and Models of chemical evolution
- Author
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Caroline Soubiran, Christian Ritter, Nina Basak, Benoit Côté, Benjamin Wehmeyer, Adam Paul, C. J. Jordan, V. V. Kovtyukh, Falk Herwig, Brad K. Gibson, T. I. Gorbaneva, Claudia Travaglio, Marco Pignatari, S. A. Korotin, Friedrich-Karl Thielemann, T. V. Mishenina, Sara Bisterzo, Astronomical Observatory of Odessa, National University and Isaac Newton Institute of Chile, M2A 2018, Laboratoire d'Astrophysique de Bordeaux [Pessac] ( LAB ), Université de Bordeaux ( UB ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Bordeaux ( UB ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Astronomical observatory of Odessa National University [Odessa], Odessa National I.I.Mechnikov University, Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), and Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Physics ,010308 nuclear & particles physics ,[ SDU.ASTR.IM ] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM] ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Galaxy ,[SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM] ,Chemical evolution ,Stars ,Stellar nucleosynthesis ,Space and Planetary Science ,0103 physical sciences ,Galaxy formation and evolution ,High resolution spectra ,010303 astronomy & astrophysics ,Chemical composition ,ComputingMilieux_MISCELLANEOUS - Abstract
We present an in-depth study of metal-poor stars, based high resolution spectra combined with newly released astrometric data from Gaia, with special attention to observational uncertainties. The results are compared to those of other studies, including Gaia benchmark stars. Chemical evolution models are discussed, highlighting few puzzles that are still affecting our understanding of stellar nucleosynthesis and of the evolution of our Galaxy.
- Published
- 2017
8. Stellar ( n,γ ) cross sections of Na23
- Author
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Sara Bisterzo, Marco Pignatari, Alberto Mengoni, F. Käppeler, Michael Wiescher, C. Lederer, E. Uberseder, and Matthias Heil
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Nuclear physics ,Physics ,010308 nuclear & particles physics ,Nucleosynthesis ,0103 physical sciences ,Resonance ,Neutron spectra ,Atomic physics ,Activation method ,010306 general physics ,s-process ,01 natural sciences - Abstract
The cross section of the $^{23}\mathrm{Na}(n,\ensuremath{\gamma})^{24}\mathrm{Na}$ reaction was measured via the activation method at the Karlsruhe 3.7 MV Van de Graaff accelerator. NaCl samples were exposed to quasistellar neutron spectra at $kT=5.1$ and 25 keV produced via the $^{18}\mathrm{O}(p,n)^{18}\mathrm{F}$ and $^{7}\mathrm{Li}(p,n)^{7}\mathrm{Be}$ reactions, respectively. The derived capture cross sections ${\ensuremath{\langle}\ensuremath{\sigma}\ensuremath{\rangle}}_{\mathrm{kT}=5\phantom{\rule{0.16em}{0ex}}\mathrm{keV}}=9.1\ifmmode\pm\else\textpm\fi{}0.3$ mb and ${\ensuremath{\langle}\ensuremath{\sigma}\ensuremath{\rangle}}_{\mathrm{kT}=25\phantom{\rule{0.16em}{0ex}}\mathrm{keV}}=2.03\ifmmode\pm\else\textpm\fi{}0.05$ mb are significantly lower than reported in literature. These results were used to substantially revise the radiative width of the first $^{23}\mathrm{Na}$ resonance and to establish an improved set of Maxwellian average cross sections. The implications of the lower capture cross section for current models of $s$-process nucleosynthesis are discussed.
- Published
- 2017
9. Galactic Chemical Evolution: the Impact of the 13C-pocket Structure on the s-process Distribution
- Author
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R. Gallino, Sara Bisterzo, Michael Wiescher, F. Käppeler, and Claudia Travaglio
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Physics ,Field (physics) ,Structure (category theory) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Galaxy ,Stars ,Distribution (mathematics) ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,0103 physical sciences ,Galaxy formation and evolution ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,010306 general physics ,s-process ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
The solar s-process abundances have been analyzed in the framework of a Galactic Chemical Evolution (GCE) model. The aim of this work is to implement the study by Bisterzo et al. (2014), who investigated the effect of one of the major uncertainties of asymptotic giant branch (AGB) yields, the internal structure of the 13C pocket. We present GCE predictions of s-process elements computed with additional tests in the light of the suggestions provided in recent publications. The analysis is extended to different metallicities, by comparing GCE results and updated spectroscopic observations of unevolved field stars. We verify that the GCE predictions obtained with different tests may represent, on average, the evolution of selected neutron-capture elements in the Galaxy. The impact of an additional weak s-process contribution from fast-rotating massive stars is also explored., Comment: 36 pages, 7 figures, 2 tables, accepted
- Published
- 2017
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10. Stellar neutron capture cross sections ofK41andSc45
- Author
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Michael Heil, Ralf Plag, Ethan Uberseder, Sara Bisterzo, Alberto Mengoni, Marco Pignatari, and F. Käppeler
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Physics ,Light nucleus ,Isotope ,010308 nuclear & particles physics ,01 natural sciences ,law.invention ,Nuclear physics ,Neutron capture ,Stars ,law ,Nucleosynthesis ,0103 physical sciences ,Van de Graaff generator ,Neutron ,Activation method ,010303 astronomy & astrophysics - Abstract
The neutron capture cross sections of light nuclei ($Al56$) are important for $s$-process scenarios since they act as neutron poisons. We report on measurements of the neutron capture cross sections of $^{41}\mathrm{K}$ and $^{45}\mathrm{Sc}$, which were performed at the Karlsruhe 3.7 MV Van de Graaff accelerator via the activation method in a quasistellar neutron spectrum corresponding to a thermal energy of $kT=25$ keV. Systematic effects were controlled by repeated irradiations, resulting in overall uncertainties of less than 3%. The measured spectrum-averaged data have been used to normalize the energy-dependent $(n,\ensuremath{\gamma})$ cross sections from the main data libraries JEFF-3.2, JENDL-4.0, and ENDF/B-VII.1, and a set of Maxwellian averaged cross sections was calculated for improving the $s$-process nucleosynthesis yields in AGB stars and in massive stars. At $kT=30$ keV, the new Maxwellian averaged cross sections of $^{41}\mathrm{K}$ and $^{45}\mathrm{Sc}$ are $19.2\ifmmode\pm\else\textpm\fi{}0.6$ mb and $61.3\ifmmode\pm\else\textpm\fi{}1.8$ mb, respectively. Both values are 20% lower than previously recommended. The effect of neutron poisons is discussed for nuclei with $Al56$ in general and for the investigated isotopes in particular.
- Published
- 2016
11. Probing astrophysically important states in theMg26nucleus to study neutron sources for thesprocess
- Author
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Xiao Fang, Y. Fujita, Hisanori Fujita, Joachim Görres, Richard deBoer, T. Adachi, Atsushi Tamii, Michael Wiescher, Sara Bisterzo, T. Itoh, T. Kadoya, Marco Pignatari, Kichiji Hatanaka, Y. Shimbara, M. Yosoi, K. Miki, A. Long, Bin Li, Tetsuya Yamamoto, G. P. A. Berg, D. Patel, R. Talwar, and Manoel Couder
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Physics ,010308 nuclear & particles physics ,Scattering ,Coulomb barrier ,01 natural sciences ,7. Clean energy ,Resonance (particle physics) ,Nuclear physics ,13. Climate action ,Nucleosynthesis ,0103 physical sciences ,Production (computer science) ,Neutron ,Atomic physics ,010306 general physics ,s-process ,Energy (signal processing) - Abstract
Background: The $^{22}\mathrm{Ne}(\ensuremath{\alpha},n)^{25}\mathrm{Mg}$ reaction is the dominant neutron source for the slow neutron capture process ($s$ process) in massive stars, and contributes, together with $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$, to the production of neutrons for the $s$ process in asymptotic giant branch (AGB) stars. However, the reaction is endothermic and competes directly with $^{22}\mathrm{Ne}(\ensuremath{\alpha},\ensuremath{\gamma})^{26}\mathrm{Mg}$ radiative capture. The uncertainties for both reactions are large owing to the uncertainty in the level structure of $^{26}\mathrm{Mg}$ near the $\ensuremath{\alpha}$ and neutron separation energies. These uncertainties affect the $s$-process nucleosynthesis calculations in theoretical stellar models.Purpose: Indirect studies in the past have been successful in determining the energies and the $\ensuremath{\gamma}$-ray and neutron widths of the $^{26}\mathrm{Mg}$ states in the energy region of interest. But, the high Coulomb barrier hinders a direct measurement of the resonance strengths, which are determined by the $\ensuremath{\alpha}$ widths for these states. The goal of the present experiments is to identify the critical resonance states and to precisely measure the $\ensuremath{\alpha}$ widths by $\ensuremath{\alpha}$-transfer techniques.Methods: The $\ensuremath{\alpha}$-inelastic scattering and $\ensuremath{\alpha}$-transfer measurements were performed on a solid $^{26}\mathrm{Mg}$ target and a $^{22}\mathrm{Ne}$ gas target, respectively, using the Grand Raiden Spectrometer at the Research Center for Nuclear Physics in Osaka, Japan. The $(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}})$ measurements were performed at $0.{45}^{\ensuremath{\circ}}, 4.{1}^{\ensuremath{\circ}}, 8.{6}^{\ensuremath{\circ}}$, and $11.{1}^{\ensuremath{\circ}}$ and the $(^{6}\mathrm{Li},d)$ measurements at ${0}^{\ensuremath{\circ}}$ and ${10}^{\ensuremath{\circ}}$. The scattered $\ensuremath{\alpha}$ particles and deuterons were detected by the focal plane detection system consisting of multiwire drift chambers and plastic scintillators. The focal plane energy calibration allowed the study of $^{26}\mathrm{Mg}$ levels from ${E}_{x}$ = 7.69--12.06 MeV in the $(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}})$ measurement and ${E}_{x}$ = 7.36--11.32 MeV in the $(^{6}\mathrm{Li},d)$ measurement.Results: Six levels (${E}_{x}$ = 10717, 10822, 10951, 11085, 11167, and 11317 keV) were observed above the $\ensuremath{\alpha}$ threshold in the region of interest (10.61--11.32 MeV). The $\ensuremath{\alpha}$ widths were calculated for these states from the experimental data. The results were used to determine the $\ensuremath{\alpha}$-capture induced reaction rates.Conclusion: The energy range above the $\ensuremath{\alpha}$ threshold in $^{26}\mathrm{Mg}$ was investigated using a high resolution spectrometer. A number of states were observed for the first time in $\ensuremath{\alpha}$-scattering and $\ensuremath{\alpha}$-transfer reactions. The excitation energies and spin-parities were determined. Good agreement is observed for previously known levels in $^{26}\mathrm{Mg}$. From the observed resonance levels the ${E}_{x}$ = 10717 keV state has a negligible contribution to the $\ensuremath{\alpha}$-induced reaction rates. The rates are dominated in both reaction channels by the resonance contributions of the states at ${E}_{x}$ = 10951, 11167, and 11317 keV. The ${E}_{x}$ = 11167 keV state has the most appreciable impact on the $(\ensuremath{\alpha},\ensuremath{\gamma})$ rate and therefore plays an important role in the prediction of the neutron production in $s$-process environments.
- Published
- 2016
12. GCE AND SOLAR S-PROCESS ABUNDANCES: DEPENDENCE ON THE 13C-POCKET STRUCTURE
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Roberto Gallino, Kaeppeler Franz, Sara Bisterzo, Claudia Travaglio, and Michael Wiescher
- Subjects
Physics ,Structure (category theory) ,Thermodynamics ,s-process - Published
- 2015
13. The s-process in low-metallicity stars - II. Interpretation of high-resolution spectroscopic observations with asymptotic giant branch models
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Sergio Cristallo, F. Kaeppeler, R. Gallino, Sara Bisterzo, and Oscar Straniero
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Physics ,Stars ,Space and Planetary Science ,Nucleosynthesis ,Metallicity ,High resolution ,Asymptotic giant branch ,Astronomy and Astrophysics ,Astrophysics ,s-process ,Low Mass ,Interpretation (model theory) - Abstract
High-resolution spectroscopic observations of a hundred metal-poor Carbon and s-rich stars (CEMP-s) collected from the literature are compared with the theoretical nucleosynthesis models of asymptotic giant branch (AGB) presented in Paper I (M = 1.3, 1.4, 1.5, 2 Msun, -3.6 < [Fe/H] < -1.5). The s-process enhancement detected in these objects is associated to binary systems: the more massive companion evolved faster through the thermally pulsing AGB phase (TP-AGB), synthesising in the inner He-intershell the s-elements, which are partly dredged-up to the surface during the third dredge-up (TDU) episode. The secondary observed low mass companion became CEMP-s by mass transfer of C and s-rich material from the primary AGB. We analyse the light elements as C, N, O, Na and Mg, as well as the two s-process indicators, [hs/ls] (where ls = is the the light-s peak at N = 50 and hs = the heavy-s peak at N = 82), and [Pb/hs]. We distinguish between CEMP-s with high s-process enhancement, [hs/Fe] > 1.5 (CEMP-sII), and mild s-process enhanced stars, [hs/Fe] < 1.5 (CEMP-sI). To interpret the observations, .... . Detailed analyses for individual stars will be provided in Paper III.
- Published
- 2011
14. Thesprocess: Nuclear physics, stellar models, and observations
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F. Käppeler, Sara Bisterzo, Roberto Gallino, and Wako Aoki
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Physics ,Stellar mass ,Metallicity ,General Physics and Astronomy ,Astronomy ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Nuclear physics ,Stars ,Nucleosynthesis ,Stellar mass loss ,Stellar physics ,Astrophysics::Solar and Stellar Astrophysics ,Asymptotic giant branch ,Stellar evolution ,Astrophysics::Galaxy Astrophysics - Abstract
Nucleosynthesis in the $s$ process takes place in the He-burning layers of low-mass asymptotic giant branch (AGB) stars and during the He- and C-burning phases of massive stars. The $s$ process contributes about half of the element abundances between Cu and Bi in solar system material. Depending on stellar mass and metallicity the resulting $s$-abundance patterns exhibit characteristic features, which provide comprehensive information for our understanding of the stellar life cycle and for the chemical evolution of galaxies. The rapidly growing body of detailed abundance observations, in particular, for AGB and post-AGB stars, for objects in binary systems, and for the very faint metal-poor population represents exciting challenges and constraints for stellar model calculations. Based on updated and improved nuclear physics data for the $s$-process reaction network, current models are aiming at an ab initio solution for the stellar physics related to convection and mixing processes. Progress in the intimately related areas of observations, nuclear and atomic physics, and stellar modeling is reviewed and the corresponding interplay is illustrated by the general abundance patterns of the elements beyond iron and by the effect of sensitive branching points along the $s$-process path. The strong variations of the $s$-process efficiency with metallicity bear also interesting consequences for galactic chemical evolution.
- Published
- 2011
15. THE WEAKs-PROCESS IN MASSIVE STARS AND ITS DEPENDENCE ON THE NEUTRON CAPTURE CROSS SECTIONS
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Sara Bisterzo, Michael Heil, F. Käppeler, Falk Herwig, Roberto Gallino, Marco Pignatari, and Michael Wiescher
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Physics ,Nuclear reaction ,education.field_of_study ,Isotopes of copper ,Metallicity ,Population ,Astronomy and Astrophysics ,Nuclear physics ,Neutron capture ,Space and Planetary Science ,Nucleosynthesis ,Astrophysics::Solar and Stellar Astrophysics ,Neutron ,s-process ,education ,Astrophysics::Galaxy Astrophysics - Abstract
The slow neutron capture process in massive stars (weak s process) produces most of the s-process isotopes between iron and strontium. Neutrons are provided by the 22Ne(?,n)25Mg reaction, which is activated at the end of the convective He-burning core and in the subsequent convective C-burning shell. The s-process-rich material in the supernova ejecta carries the signature of these two phases. In the past years, new measurements of neutron capture cross sections of isotopes beyond iron significantly changed the predicted weak s-process distribution. The reason is that the variation of the Maxwellian-averaged cross sections (MACS) is propagated to heavier isotopes along the s path. In the light of these results, we present updated nucleosynthesis calculations for a 25 M ? star of Population I (solar metallicity) in convective He-burning core and convective C-burning shell conditions. In comparison with previous simulations based on the Bao et?al. compilation, the new measurement of neutron capture cross sections leads to an increase of s-process yields from nickel up to selenium. The variation of the cross section of one isotope along the s-process path is propagated to heavier isotopes, where the propagation efficiency is higher for low cross sections. New 74Ge, 75As, and 78Se MACS result in a higher production of germanium, arsenic, and selenium, thereby reducing the s-process yields of heavier elements by propagation. Results are reported for the He core and for the C shell. In shell C-burning, the s-process nucleosynthesis is more uncertain than in the He core, due to higher MACS uncertainties at higher temperatures. We also analyze the impact of using the new lower solar abundances for CNO isotopes on the s-process predictions, where CNO is the source of 22Ne, and we show that beyond Zn this is affecting the s-process yields more than nuclear or stellar model uncertainties considered in this paper. In particular, using the new updated initial composition, we obtain a high s-process production (overproduction higher than 16O, ~100) for Cu, Ga, Ge, and As. Using the older abundances by Anders & Grevesse, also Se, Br, Kr, and Rb are efficiently produced. Our results have important implications in explaining the origin of copper in the solar abundance distribution, pointing to a prevailing contribution from the weak s-process in agreement with spectroscopic observations and Galactic chemical evolution calculations. Because of the improvement due to the new MACS for nickel and copper isotopes, the nucleosynthesis of copper is less affected by nuclear uncertainties compared to heavier s-process elements. An experimental determination of the 63Ni MACS is required for a further improvement of the abundance prediction of copper. The available spectroscopic observations of germanium and gallium in stars are also discussed, where most of the cosmic abundances of these elements derives from the s-process in massive stars.
- Published
- 2010
16. The Hobby‐Eberly Telescope Chemical Abundances of Stars in the Halo (CASH) Project. I. The Lithium‐,s‐, andr‐enhanced Metal‐poor Giant HKII 17435−00532
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Christopher Sneden, Roberto Gallino, Matthew Shetrone, Timothy C. Beers, Anna Frebel, Carlos Allende Prieto, Ian U. Roederer, John J. Cowan, Jaehyon Rhee, and Sara Bisterzo
- Subjects
Physics ,Astrophysics (astro-ph) ,FOS: Physical sciences ,chemistry.chemical_element ,Astronomy and Astrophysics ,Astrophysics ,Horizontal branch ,Red-giant branch ,Radial velocity ,Stars ,chemistry ,Space and Planetary Science ,Hobby–Eberly Telescope ,Asymptotic giant branch ,Lithium ,Halo - Abstract
We present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project "Chemical Abundances of Stars in the Halo" (CASH). A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R~15,000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H]=-2.2) star has an unusually high lithium abundance (log eps (Li)=+2.1), mild carbon ([C/Fe]=+0.7) and sodium ([Na/Fe]=+0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe]=+0.8) and r-process ([Eu/Fe]=+0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing that connects the convective envelope with the outer regions of the H-burning shell. If so, HKII 17435-00532 is the most metal-poor star in which this short-lived phase of Li enrichment has been observed. The Na and n-capture enrichment can be explained by mass transfer from a companion that passed through the thermally-pulsing AGB phase of evolution with only a small initial enrichment of r-process material present in the birth cloud. Despite the current non-detection of radial velocity variations (over ~180 days), it is possible that HKII 17435-00532 is in a long-period or highly-inclined binary system, similar to other stars with similar n-capture enrichment patterns., 29 pages, 8 figures. Accepted for publication in ApJ. A full version of table 3 is available from the first author upon request
- Published
- 2008
17. 176Lu/176Hf: A Sensitive Test ofs‐Process Temperature and Neutron Density in AGB Stars
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Nicolas Winckler, Sara Bisterzo, Saed Dababneh, Thomas Rauscher, K. Wisshak, R. Gallino, Michael Heil, F. Käppeler, and Andrew M. Davis
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Nuclear reaction ,Physics ,Isotope ,Astronomy and Astrophysics ,Neutron temperature ,law.invention ,Semiconductor detector ,Nuclear physics ,Stars ,Space and Planetary Science ,law ,Nucleosynthesis ,Van de Graaff generator ,s-process - Abstract
The s-process branching at A ¼ 176 has been analyzed on the basis of significantly improved experimental cross sections.Thisworkreportsonactivationmeasurementsofthepartial(n ;� )crosssectionof 176Lufeedingtheisomeric state in 176 Lu. In total, six irradiations were performed at the Karlsruhe 3.7 MV pulsed Van de Graaff accelerator, and the induced activities were measured with HPGe clover detectors. In combination with previous data, partial cross sections of 3185 � 156 and 1153 � 30 mbarn were deduced at kT ¼ 5:1 and 25 keV, respectively. With these results and a recent time-of-flight measurement of the total stellar (n ;� ) cross section, the isomeric ratio was found to be constant in the relevant thermal energy range of the main s-process component. Based on these new data, a comprehensive analysis of the branching at 176 Lu was carried out for testing the temperature and neutron density conditions duringHeshellflashesinthermallypulsinglow-massasymptoticgiantbranchstars.Itwasfoundthatthelong-standing problem of the mother/daughter ratio of the two s-only isotopes 176 Lu and 176 Hf could be solved, if the temperaturedependent � -decay half-life of 176 Lu was considered with sufficient resolution over the temperature profile of the
- Published
- 2008
18. Erratum: Stellar neutron capture cross sections ofNe20,21,22[Phys. Rev. C90, 045804 (2014)]
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R. Gallino, Ralf Plag, Matthias Heil, A. Mengoni, C. Lederer, Marco Pignatari, F. Käppeler, E. Uberseder, A. Juseviciute, and Sara Bisterzo
- Subjects
Physics ,Nuclear and High Energy Physics ,Neutron capture ,Radiative capture ,Atomic physics ,s-process - Published
- 2015
19. The branchings of the main s-process: their sensitivity to α-induced reactions on 13C and 22Ne and to the uncertainties of the nuclear network
- Author
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Gianluca Imbriani, Richard deBoer, R. Gallino, Sara Bisterzo, F. Käppeler, Joachim Görres, Oscar Straniero, Sergio Cristallo, Michael Wiescher, ITA, USA, DEU, Bisterzo, S., Gallino, R., Käppeler, F., Wiescher, M., Imbriani, Gianluca, Straniero, O., Cristallo, S., Görres, J., and Deboer, R. J.
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Physics ,Nuclear reaction ,Stars: abundance ,Isotope ,Nuclear Theory ,Stars: AGB and post-AGB ,FOS: Physical sciences ,Astronomy and Astrophysics ,Nuclear physics ,Neutron capture ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Nucleosynthesis ,Stars: low-ma ,Astrophysics::Solar and Stellar Astrophysics ,Neutron source ,Neutron ,Nuclide ,Nuclear reactions, nucleosynthesis, abundance ,Atomic physics ,Nuclear Experiment ,s-process ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
This paper provides a detailed analysis of the main component of the slow neutron capture process (the s-process), which accounts for the solar abundances of half of the nuclei with 90, Comment: 43 pages, 17 Figures, 4 Tables, Supporting Information
- Published
- 2015
20. Correlated Strontium and Barium Isotopic Compositions of Acid-Cleaned Single Silicon Carbides from Murchison
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Michael J. Pellin, Michael R. Savina, Iris Dillmann, Sara Bisterzo, Roberto Gallino, Sergio Cristallo, Nicolas Dauphas, Frank Gyngard, F. Käppeler, Nan Liu, Andrew M. Davis, ITA, USA, DEU, and CAN
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Murchison meteorite ,Physics ,Strontium ,Silicon ,Analytical chemistry ,chemistry.chemical_element ,FOS: Physical sciences ,Astronomy and Astrophysics ,Barium ,Giant star ,Astrophysics - Solar and Stellar Astrophysics ,chemistry ,Space and Planetary Science ,Nucleosynthesis ,Asymptotic giant branch ,s-process ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
We present strontium, barium, carbon, and silicon isotopic compositions of 61 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing both strontium and barium contamination. For the first time, by using correlated $^{88}Sr$/$^{86}Sr$ and $^{138}Ba$/$^{136}Ba$ ratios in mainstream SiC grains, we are able to resolve the effect of $^{13}C$ concentration from that of $^{13}C$-pocket mass on s-process nucleosynthesis, which points towards the existence of large $^{13}C$-pockets with low $^{13}C$ concentration in AGB stars. The presence of such large $^{13}$R-pockets with a variety of relatively low $^{13}C$ concentrations seems to require multiple mixing processes in parent AGB stars of mainstream SiC grains.
- Published
- 2015
- Full Text
- View/download PDF
21. Carbon-enhanced Metal-poor Stars: Osmium and Iridium Abundances in the Neutron-Capture-enhanced Subgiants CS 31062-050 and LP 625-44
- Author
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Sara Bisterzo, Sean G. Ryan, Stelios Tsangarides, Wako Aoki, Timothy C. Beers, Roberto Gallino, and John E. Norris
- Subjects
Physics ,Astrophysics (astro-ph) ,FOS: Physical sciences ,chemistry.chemical_element ,Astronomy and Astrophysics ,Barium ,Astrophysics ,Stars ,chemistry ,Space and Planetary Science ,Abundance (ecology) ,Nucleosynthesis ,Asymptotic giant branch ,Osmium ,Iridium ,Europium - Abstract
We have investigated the abundances of heavy neutron-capture elements, including osmium (Os) and iridium (Ir), in the two Carbon-Enhanced Metal-Poor (CEMP) subgiants CS31062-050 and LP625-44. CS31062-050 is known to be a so-called CEMP-r/s star, which exhibits large excesses of s-process elements such as barium (Ba) and lead (Pb), as well as a significant enhancement of europium (Eu) that cannot be explained by conventional s-process production in Asymptotic Giant Branch star models. Our analysis of the high-resolution spectrum for this object has determined, for the first time, the abundances of Ir and Os, elements in the third peak of the r-process nucleosynthesis. They also exhibit significant excesses relative to the predictions of standard s-process calculations. These two elements are not detected in a similar-quality spectrum of LP625-44; the derived upper limits on their abundances are lower than the abundances in CS31062-050. We compare the observed abundance patterns of neutron-capture elements, including Os and Ir, in these two stars with recent model calculations of the s-process, and discuss possible interpretations., Comment: 12 pages, 2 figures, 1 table, ApJ Letter, in press
- Published
- 2006
22. Near‐Ultraviolet Observations of HD 221170: New Insights into the Nature ofr‐Process–rich Stars
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James E. Lawler, Roberto Gallino, Christopher Sneden, Jennifer Simmerer, Sara Bisterzo, Inese I. Ivans, and John J. Cowan
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Physics ,Solar System ,Red giant ,Stellar atmosphere ,Sigma ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Stars ,Space and Planetary Science ,Abundance (ecology) ,0103 physical sciences ,r-process ,010306 general physics ,010303 astronomy & astrophysics ,Chemical composition - Abstract
Employing high resolution spectra obtained with the near-UV sensitive detector on the Keck I HIRES, supplemented by data obtained with the McDonald Observatory 2-d coude, we have performed a comprehensive chemical composition analysis of the bright r-process-rich metal-poor red giant star HD221170. Analysis of 57 individual neutral and ionized species yielded abundances for a total of 46 elements and significant upper limits for an additional five. Model stellar atmosphere parameters were derived with the aid of ~200 Fe-peak transitions. From more than 350 transitions of 35 neutron-capture (Z > 30) species, abundances for 30 neutron-capture elements and upper limits for three others were derived. Utilizing 36 transitions of La, 16 of Eu, and seven of Th, we derive ratios of log epsilon(Th/La) = -0.73 (sigma = 0.06) and log epsilon(Th/Eu) = -0.60 (sigma = 0.05), values in excellent agreement with those previously derived for other r-process-rich metal-poor stars such as CS22892-052, BD+17 3248, and HD115444. Based upon the Th/Eu chronometer, the inferred age is 11.7 +/- 2.8 Gyr. The abundance distribution of the heavier neutron-capture elements (Z >= 56) is fit well by the predicted scaled solar system r-process abundances, as also seen in other r-process-rich stars. Unlike other r-process-rich stars, however, we find that the abundances of the lighter neutron-capture elements (37 < Z < 56) in HD221170 are also statistically in better agreement with the abundances predicted for the scaled solar r-process pattern.
- Published
- 2006
23. Stellar neutron capture cross sections ofNe20,21,22
- Author
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Roberto Gallino, Marco Pignatari, A. Juseviciute, F. Käppeler, Sara Bisterzo, Alberto Mengoni, Michael Heil, Ralf Plag, Ethan Uberseder, and C. Lederer
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Physics ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Red giant ,Radiative capture ,7. Clean energy ,01 natural sciences ,Resonance (particle physics) ,Nuclear physics ,Neutron capture ,Stars ,0103 physical sciences ,Neutron ,s-process ,010303 astronomy & astrophysics - Abstract
The stellar $(n,\ensuremath{\gamma})$ cross sections of the Ne isotopes are important for a number of astrophysical quests, i.e., for the interpretation of abundance patterns in presolar material or with respect to the $s$-process neutron balance in red giant stars. This paper presents resonance studies of experimental data in the keV range, which had not been fully analyzed before. The analyses were carried out with the $\mathcal{R}$-matrix code sammy. With these results for the resonant part and by adding the components due to direct radiative capture, improved Maxwellian-averaged cross sections (MACS) could be determined. At $kT=30\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$ thermal energy we obtain MACS values of $240\ifmmode\pm\else\textpm\fi{}29,\phantom{\rule{0.16em}{0ex}}1263\ifmmode\pm\else\textpm\fi{}160$, and $53.2\ifmmode\pm\else\textpm\fi{}2.7 \ensuremath{\mu}\mathrm{barn}$ for $^{20}\mathrm{Ne},\phantom{\rule{0.16em}{0ex}}^{21}\mathrm{Ne}$, and $^{22}\mathrm{Ne}$, respectively. In earlier work the stellar rates of $^{20}\mathrm{Ne}$ and $^{21}\mathrm{Ne}$ had been grossly overestimated. $^{22}\mathrm{Ne}$ and $^{20}\mathrm{Ne}$ are significant neutron poisons for the $s$ process in stars because their very small MACS values are compensated by their large abundances.
- Published
- 2014
24. Cu and Zn in different stellar populations: Inferring their astrophysical origin
- Author
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Verne V. Smith, Sara Bisterzo, K. Cunha, Alexander Heger, Marco Pignatari, L. Pompeia, and R. Gallino
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Physics ,Galactic halo ,Nuclear and High Energy Physics ,Stars ,Supernova ,Stellar nucleosynthesis ,Nucleosynthesis ,Globular cluster ,Astronomy ,Neutron ,Astrophysics ,Omega - Abstract
Copper and Zinc behave differently in unevolved stars of various metallicities and stellar populations. Current hypotheses on the astrophysical origin of both elements are highly debated. It has been advanced in previous works ([Matteucci, F., Raiteri, C., Busso, M., Gallino, R. and Gratton, R. A&A 272 (1993) 421,Mishenina, T.V. et al. A&A 396 (2002) 189]) that most solar Cu and Zn were synthesized in Type la Supernovae, although present theory of SNIe explosions predicts very little contribution to both elements [Thielemann, F.-K., Nomoto, K. and Yokoi, K. A&A 158 (1986) 17]. We have collected a large sample of recent high-resolution spectroscopic observations of unevolved stars in the Galactic halo, thick-disk and thin-disk, in bulge-like stars, globular clusters, Omega Cen, and Dwarf Spheroidal systems. Then we compare spectroscopic observations of Cu and Zn with present stellar nucleosynthesis theory. Cu is the best signature of a secondary-like production in massive stars by neutron captures with a small primary contribution by explosive nucleosynthesis. Zn needs a more complex description. No need of extra contribution by SNIa is required.
- Published
- 2005
25. CS29497-030 Abundance Constraints on Neutron-Capture Nucleosynthesis
- Author
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Roberto Gallino, John J. Cowan, George W. Preston, Sara Bisterzo, Inese I. Ivans, and Christopher Sneden
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Physics ,T Tauri star ,Supernova ,Stellar nucleosynthesis ,Space and Planetary Science ,Star formation ,Abundance (ecology) ,Molecular cloud ,Stellar mass loss ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Blue straggler - Abstract
Chemical abundances and upper limits of three dozen elements have been derived for the binary blue metal-poor, extremely lead-rich star CS29497-030. The findings include a large contribution of s-process material (e.g., [Pb/Fe] >3.5) and a large contribution of r-process material (e.g, [Eu/Fe] ∼2), abundances which place it in the class of objects known as r+s stars. The ratio of [Zr/Nb] ∼0, along with its stellar parameters, indicates that it is not an intrinsic AGB star. Modelling the abundance distribution (which includes the first Bi abundance determination for any metal-poor star) with s-process calculations employing FRANEC models, there is excellent agreement with the observations by adopting a 1.3 M[odot ] AGB model with an enhanced 13C-pocket and a pre-enrichment of r-process material. In this scenario, the initial abundances of CS29497-030 and its binary partner arose from a parent cloud with an extreme r-process abundance, in which star formation was triggered by a core-collapse supernova which polluted, snowplowed, and clumped a nearby molecular cloud. Pollution from the former AGB star's dredged-up material subsequently enriched the envelope composition of CS29497-030 (Ivans et al. 2005). Critical tests of this model and scenario include the dependence of abundance ratios on systematics due to non-LTE effects, the choice of stellar parameters and model atmospheres, and the assumed abundance pattern of the protostellar cloud out of which the CS29497-030 binary system formed.
- Published
- 2005
26. The 13C-Pocket Structure in AGB Models: Constraints from Zirconium Isotope Abundances in Single Mainstream SiC Grains
- Author
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Andrew M. Davis, Roberto Gallino, Sara Bisterzo, Michael R. Savina, Nan Liu, and Michael J. Pellin
- Subjects
Physics ,Isotope ,chemistry.chemical_element ,FOS: Physical sciences ,Astronomy and Astrophysics ,Barium ,Astrophysics ,Nuclear physics ,Astrophysics - Solar and Stellar Astrophysics ,chemistry ,Space and Planetary Science ,Nucleosynthesis ,Isotopes of zirconium ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
We present postprocess AGB nucleosynthesis models with different $^{13}$C-pocket internal structures to better explain zirconium isotope measurements in mainstream presolar SiC grains by Nicolussi et al. (1997) and Barzyk et al. (2007). We show that higher-than-solar $^{92}$Zr/$^{94}$Zr ratios can be predicted by adopting a $^{13}$C-pocket with a flat $^{13}$C profile, instead of the previous decreasing-with-depth $^{13}$C profile. The improved agreement between grain data for zirconium isotopes and AGB models provides additional support for a recent proposal of a flat $^{13}$C profile based on barium isotopes in mainstream SiC grains by Liu et al. (2014).
- Published
- 2014
- Full Text
- View/download PDF
27. Impact of Nuclear Reaction Uncertainties on AGB Nucleosynthesis Models
- Author
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Claudia Travaglio, Sara Bisterzo, Kaeppeler Franz, Roberto Gallino, and Michael Wiescher
- Subjects
Nuclear physics ,Nuclear reaction ,Physics ,Astrophysics - Solar and Stellar Astrophysics ,Nucleosynthesis ,FOS: Physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
Asymptotic giant branch (AGB) stars with low initial mass (1 - 3 Msun) are responsible for the production of neutron-capture elements through the main s-process (main slow neutron capture process). The major neutron source is 13C(alpha, n)16O, which burns radiatively during the interpulse periods at about 8 keV and produces a rather low neutron density (10^7 n/cm^3). The second neutron source 22Ne(alpha, n)25Mg, partially activated during the convective thermal pulses when the energy reaches about 23 keV, gives rise to a small neutron exposure but a peaked neutron density (Nn(peak) > 10^11 n/cm^3). At metallicities close to solar, it does not substantially change the final s-process abundances, but mainly affects the isotopic ratios near s-path branchings sensitive to the neutron density. We examine the effect of the present uncertainties of the two neutron sources operating in AGB stars, as well as the competition with the 22Ne(alpha, gamma)26Mg reaction. The analysis is carried out on AGB the main-s process component (reproduced by an average between M(AGB; ini) = 1.5 and 3 Msun at half solar metallicity, see Arlandini et al. 1999), using a set of updated nucleosynthesis models. Major effects are seen close to the branching points. In particular, 13C(alpha, n)16O mainly affects 86Kr and 87Rb owing to the branching at 85Kr, while small variations are shown for heavy isotopes by decreasing or increasing our adopted rate by a factor of 2 - 3. By changing our 22Ne(alpha, n)25Mg rate within a factor of 2, a plausible reproduction of solar s-only isotopes is still obtained. We provide a general overview of the major consequences of these variations on the s-path. A complete description of each branching will be presented in Bisterzo et al., in preparation., Proceedings of Science 108, XII International Symposium on Nuclei in the Cosmos 2012 (Cairns, Australia); 6 pages, 2 figures
- Published
- 2013
28. CEMP-s and CEMP-s/r stars: last update
- Author
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F. Käppeler, Oscar Straniero, R. Gallino, Sergio Cristallo, Sara Bisterzo, and Michael Wiescher
- Subjects
Physics ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Nucleosynthesis ,General Engineering ,Asymptotic giant branch ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
We provide an updated discussion of the sample of CEMP-s and CEMP-s/r stars collected from the literature. Observations are compared with the theoretical nucleosynthesis models of asymptotic giant branch (AGB) stars presented by Bisterzo et al. (2010, 2011, 2012), in the light of the most recent spectroscopic results., Comment: 10 pages, 2 figures, New advances in stellar physics: from microscopic to macroscopic processes, May 27-31 2013, Roscoff, France, EDP Science, EAS Publications Series, in press
- Published
- 2013
- Full Text
- View/download PDF
29. Neutron capture onZr94: Resonance parameters and Maxwellian-averaged cross sections
- Author
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Christoph A. Stephan, B. Haas, J. Marganiec, S. Andriamonje, F. Gunsing, G. Aerts, G. Cortes, Cristian Massimi, E. Chiaveri, C. Eleftheriadis, P. F. Mastinu, L. Perrot, R. Gallino, Thomas Rauscher, F. Alvarez-Velarde, C. Carrapiço, D. Karadimos, M. Rosetti, W. Dridi, A. Mengoni, N. Colonna, Roberto Capote, Gerald Badurek, Rene Reifarth, P. Cennini, A. J. M. Plompen, M. Dahlfors, Sara Bisterzo, P. Vaz, M. Embid-Segura, S. Lukic, E. Gonzalez-Romero, J. Salgado, A. Poch, A. Herrera-Martinez, N. Patronis, Aaron Couture, H. Leeb, I. Savvidis, J. M. Quesada, A. Plukis, Arnaud Ferrari, L. Tassan-Got, E. Kossionides, G. Vannini, R. C. Haight, Manuel Lozano, F. Gramegna, Marco Calviani, C. Paradela, James L. Cox, A. Pavlik, C. Domingo-Pardo, M. Mosconi, Martin Heil, K. Wisshak, Javier Praena, V. Chepel, G. Rudolf, C. T. Papadopoulos, A. Lindote, L. Audouin, M. Krtička, F. Calviño, R. Vlastou, F. Neves, P. M. Milazzo, C. Rubbia, Michael Wiescher, P. Baumann, F. Voss, S. O'Brien, E. Berthoumieux, Corrie S. Moreau, R. Ferreira-Marques, T. Martinez, A. Ventura, C. Santos, D. Villamarin, Isabel S. Gonçalves, Vasilis Vlachoudis, I. Duran, S. Marrone, D. Cano-Ott, Marco T. Pigni, R. Terlizzi, M. Kerveno, J. Andrzejewski, F. Bečvář, E. Jericha, S. David, G. Tagliente, P. Pavlopoulos, L. Tavora, Isabel Lopes, H. Álvarez, C. Lamboudis, J. L. Tain, L. Sarchiapone, K. Fujii, P. Rullhusen, Fabio Belloni, C. Pretel, Carlos Guerrero, U. Abbondanno, Heinz Oberhummer, W.I. Furman, C. A. Papachristodoulou, S. Walter, Ralf Plag, F. Käppeler, J. Pancin, D. Karamanis, I. Dillmann, Y. Kadi, and M. C. Vincente
- Subjects
Nuclear reaction ,Physics ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,7. Clean energy ,01 natural sciences ,Neutron temperature ,Nuclear physics ,Neutron capture ,0103 physical sciences ,Neutron cross section ,Neutron source ,Isotopes of zirconium ,Neutron ,Nuclear Experiment ,s-process ,010303 astronomy & astrophysics - Abstract
The neutron capture cross sections of the Zr isotopes play an important role in nucleosynthesis studies. The s-process reaction flow between the Fe seed and the heavier isotopes passes through the neutron magic nucleus {sup 90}Zr and through {sup 91,92,93,94}Zr, but only part of the flow extends to {sup 96}Zr because of the branching point at {sup 95}Zr. Apart from their effect on the s-process flow, the comparably small isotopic (n,{gamma}) cross sections make Zr also an interesting structural material for nuclear reactors. The {sup 94}Zr (n,{gamma}) cross section has been measured with high resolution at the spallation neutron source n{sub T}OF at CERN and resonance parameters are reported up to 60 keV neutron energy.
- Published
- 2011
30. Low Mass Stars. Evolution and Nucleosynthesis
- Author
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Roberto Gallino, Sara Bisterzo, Eduardo Telles, Renato Dupke, and Daniela Lazzaro
- Subjects
Physics ,Stellar mass ,Astrophysics::High Energy Astrophysical Phenomena ,K-type main-sequence star ,Stellar collision ,Astronomy ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,T Tauri star ,Stellar nucleosynthesis ,Nucleosynthesis ,Stellar mass loss ,Astrophysics::Solar and Stellar Astrophysics ,Asymptotic giant branch ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
This paper briefly reviews key aspects concerning the evolution and nucleosynthesis of low mass stars both in the disc and in the halo. Low mass stars contribute to the cosmic production of C and most of the heavy neutron capture elements through the s‐process. The s‐process nucleosynthesis occurs during the thermally pulsing asymptotic giant branch phase (TP‐AGB), while the star looses its whole envelope by efficient stellar winds. We will discuss significant examples of different classes of s‐enhanced stars and compare the high‐resolution spectroscopic observations with theoretical AGB models.
- Published
- 2011
31. Neutron cross sections at n_TOF
- Author
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M. Oshima, J. Andrzejewski, J. Pancin, A. Pavlik, S. Lukic, G. Cortes, B. Haas, Y. Kadi, I. Duran, Iris Dillmann, Costas G. Papadopoulos, H. Frais-Koelbl, V. Konovalov, M. Dahlfors, L. Perrot, C. Eleftheriadis, P. Vaz, K. Fujii, C. Carrapiço, Aaron Couture, F. Voss, J. Salgado, A. Poch, F. Becvar, I. Savvidis, P. Cennini, Thomas Rauscher, Roberto Capote, P.A. Assimakopoulos, W. Dridi, A. Goverdovski, Rene Reifarth, Isabel Lopes, F. Calviño, H. Leeb, Nicola Colonna, M. Embid-Segura, L. Ferrant, E. Griesmayer, G. Aerts, A. Plukis, F. Alvarez-Velarde, Vasilis Vlachoudis, H. Alvarez-Pol, L. Sarchiapone, D. Karadimos, F. Gramegna, Wiescher Michael, L. Fitzpatrick, Manuel Lozano, D. Karamanis, E. González-Romero, G. Vannini, K. Wisshak, Sara Bisterzo, R. Vlastou, Gerald Badurek, N. Patronis, J. M. Quesada, S. Andriamonje, L. Tassan-Got, E. Berthoumieux, A. Herrera-Martinez, R. Dolfini, E. Jericha, D. Villamarin, E. Chiaveri, M. Rosetti, M. C. Vincente, Arnaud Ferrari, R. Ferreira Marques, P. F. Mastinu, H. Wendler, S. David, M. Mosconi, Alberto Mengoni, C. Stephan, F. Gunsing, G. Tagliente, D. Cano-Ott, S. Isaev, S. O'Brien, V. Ketlerov, M. Krtička, P. E. Koehler, V. Chepel, G. Rudolf, F. Käppeler, Roberto Gallino, César Domingo Pardo, R. Terlizzi, C. Paradela, F. Neves, P. M. Milazzo, L. Audouin, P. Pavlopoulos, L. Tavora, J. Marganiec, P. Rullhusen, P. Baumann, C. Pretel, Masayuki Igashira, E. Kossionides, A. Lindote, Michael Heil, Carlos Guerrero, U. Abbondanno, Heinz Oberhummer, A. J. M. Plompen, S. Walter, Ralf Plag, James L. Cox, W.I. Furman, C. A. Papachristodoulou, Andrea Venturi, Corrie S. Moreau, M. Kerveno, C. Rubbia, Isabel S. Gonçalves, S. Marrone, C. Lamboudis, J. L. Tain, and Robert C. Haight
- Subjects
Nuclear physics ,Astrophysics and Astronomy ,Materials science ,Neutron - Published
- 2010
32. Measurement of the partial $(n,\gamma)$ cross section to $^{176}$Lu$^{m}$ at s-process temperatures
- Author
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Michael Heil, F. Käppeler, Sara Bisterzo, Nicolas Winckler, Roberto Gallino, and Saed Dababneh
- Subjects
Physics ,Nuclear physics ,Astrophysics and Astronomy ,Cross section (physics) ,s-process - Published
- 2010
33. Neutron physics of the Re/Os clock. I. Measurement of the (n,γ) cross sections ofOs186,187,188at the CERN n_TOF facility
- Author
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A. J. M. Plompen, L. Tavora, M. Krtička, F. Calviño, A. Pavlik, F. Voss, D. Karamanis, I. Dillmann, R. Ferreira-Marques, V. Chepel, R. C. Haight, Vasilis Vlachoudis, H. Alvarez-Pol, P. Rullhusen, G. Rudolf, C. Paradela, James L. Cox, L. Sarchiapone, S. Lukic, F. Gramegna, L. Audouin, E. Jericha, S. David, R. Gallino, Matthias Heil, G. Tagliente, J. Pancin, G. Cortes, P. Cennini, Carlos Guerrero, U. Abbondanno, Michael Wiescher, V. Ketlerov, M. Oshima, Sara Bisterzo, S. Andriamonje, E. Griesmayer, M. C. Vincente, A. Herrera-Martinez, N. Patronis, F. Bečvář, Heinz Oberhummer, Y. Kadi, E. Chiaveri, M. Embid-Segura, H. Frais-Koelbl, C. T. Papadopoulos, M. Mosconi, Arnaud Ferrari, J. Andrzejewski, P. F. Mastinu, J. Marganiec, Alberto Mengoni, P. Baumann, G. Aerts, J. Salgado, F. Käppeler, L. Perrot, Masayuki Igashira, A. Poch, G. Badurek, S. Walter, Manuel Lozano, C. Eleftheriadis, C. Rubbia, Corrie S. Moreau, S. Isaev, S. O'Brien, K. Wisshak, F. Neves, N. Colonna, F. Alvarez-Velarde, Isabel S. Gonçalves, Thomas Rauscher, P. M. Milazzo, P. E. Koehler, A. Ventura, Ralf Plag, S. Marrone, M. Dahlfors, Roberto Capote, P.A. Assimakopoulos, L. Marques, R. Terlizzi, M. Kerveno, Isabel Lopes, D. Karadimos, E. Kossionides, R. Vlastou, P. Vaz, G. Vannini, Javier Praena, D. Cano-Ott, E. Berthoumieux, I. Duran, A. Plukis, Rene Reifarth, E. González-Romero, A. Carrillo de Albornoz, W.I. Furman, I. Savvidis, J. M. Quesada, Aaron Couture, H. Wendler, L. Tassan-Got, M. Calviani, C. Domingo-Pardo, V. Konovalov, C. Stephan, B. Haas, C. Lamboudis, J. L. Tain, M. Rosetti, F. Gunsing, C. A. Papachristodoulou, W. Dridi, Cristian Massimi, H. Leeb, P. Pavlopoulos, L. Ferrant, K. Fujii, L. Fitzpatrick, D. Villamarin, Fabio Belloni, C. Pretel, A. Lindote, A. Goverdovski, and R. Dolfini
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Physics ,Nuclear reaction ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Gamma ray ,Scintillator ,01 natural sciences ,7. Clean energy ,Nuclear physics ,Neutron capture ,13. Climate action ,Nucleosynthesis ,0103 physical sciences ,Neutron ,s-process ,010303 astronomy & astrophysics ,Radioactive decay - Abstract
The precise determination of the neutron capture cross sections of Os-186 and Os-187 is important to define the s-process abundance of Os-187 at the formation of the solar system. This quantity can be used to evaluate the radiogenic component of the abundance of Os-187 due to the decay of the unstable Re-187 (t(1/2) = 41.2 Gyr) and from this to infer the time duration of the nucleosynthesis in our galaxy (Re/Os cosmochronometer). The neutron capture cross sections of Os-186, Os-187, and Os-188 have been measured at the CERN n_TOF facility from 1 eV to 1 MeV, covering the entire energy range of astrophysical interest. The measurement has been performed by time-of-flight technique using isotopically enriched samples and two C6D6 scintillation detectors for recording the prompt. rays emitted in the capture events. Maxwellian averaged capture cross sections have been determined for thermal energies between kT = 5 and 100 keV corresponding to all possible s-process scenarios. The estimated uncertainties for the values at 30 keV are 4.1, 3.3, and 4.7% for Os-186, Os-187, and Os-188, respectively.
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- 2010
34. Neutron physics of the Re/Os clock. III. Resonance analyses and stellar (n,γ) cross sections ofOs186,187,188
- Author
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D. Karamanis, I. Dillmann, V. Chepel, M. Kerveno, G. Rudolf, D. Villamarin, F. Gramegna, B. Haas, L. Tavora, M. Dahlfors, P. Pavlopoulos, R. Vlastou, E. Berthoumieux, P. Vaz, P. Baumann, E. Gonzalez-Romero, Marco Calviani, A. Lindote, J. Salgado, A. Poch, F. Bečvář, P. Rullhusen, W. Dridi, M. Oshima, A. Plukis, M. Embid-Segura, G. Cortes, F. Gunsing, Aaron Couture, Rene Reifarth, Sara Bisterzo, K. Fujii, J. Andrzejewski, L. Ferrant, J. Marganiec, M. C. Vincente, J. M. Quesada, L. Tassan-Got, A. Herrera-Martinez, N. Patronis, A. Goverdovski, F. Alvarez-Velarde, S. Andriamonje, E. Chiaveri, G. Aerts, Cristian Massimi, C. Eleftheriadis, L. Fitzpatrick, A. Pavlik, P. F. Mastinu, Gerald Badurek, Arnaud Ferrari, P. Cennini, Fabio Belloni, C. Domingo-Pardo, R. C. Haight, Christoph A. Stephan, R. Dolfini, C. T. Papadopoulos, S. Lukic, C. Paradela, Roberto Capote, M. Mosconi, L. Sarchiapone, L. Audouin, Thomas Rauscher, A. Ventura, P.A. Assimakopoulos, S. O'Brien, C. Rubbia, J. Pancin, V. Konovalov, R. Terlizzi, E. Griesmayer, M. Krtička, G. Vannini, H. Leeb, C. Pretel, Manuel Lozano, Isabel S. Gonçalves, F. Calviño, Y. Kadi, Michael Wiescher, F. Voss, H. Frais-Koelbl, D. Karadimos, L. Marques, S. Marrone, S. David, G. Tagliente, E. Jericha, R. Ferreira-Marques, Nicola Colonna, K. Wisshak, Vasilis Vlachoudis, H. Alvarez-Pol, S. Isaev, C. Lamboudis, J. L. Tain, P. E. Koehler, H. Wendler, L. Perrot, F. Käppeler, M. Rosetti, I. Duran, I. Savvidis, A. Mengoni, V. Ketlerov, A. Carrillo de Albornoz, W.I. Furman, C. A. Papachristodoulou, Carlos Guerrero, U. Abbondanno, F. Neves, Heinz Oberhummer, P. M. Milazzo, S. Walter, Ralf Plag, R. Gallino, Michael Heil, D. Cano-Ott, E. Kossionides, Corrie S. Moreau, Javier Praena, A. J. M. Plompen, I. Lopes, James L. Cox, and Masayuki Igashira
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Physics ,Nuclear reaction ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Resonance ,01 natural sciences ,7. Clean energy ,Nuclear physics ,Neutron capture ,13. Climate action ,Nucleosynthesis ,0103 physical sciences ,Neutron ,Nucleon ,s-process ,010303 astronomy & astrophysics ,Stellar evolution - Abstract
Neutron resonance analyses have been performed for the capture cross sections of Os-186, Os-187, and Os-188 measured at the n_TOF facility at CERN. Resonance parameters have been extracted up to 5, 3, and 8 keV, respectively, using the SAMMY code for a full R-matrix fit of the capture yields. From these results average resonance parameters were derived by a statistical analysis to provide a comprehensive experimental basis for modeling of the stellar neutron capture rates of these isotopes in terms of the Hauser-Feshbach statistical model. Consistent calculations for the capture and inelastic reaction channels are crucial for the evaluation of stellar enhancement factors to correct the Maxwellian averaged cross sections obtained from experimental data for the effect of thermally populated excited states. These factors have been calculated for the full temperature range of current scenarios of s-process nucleosynthesis using the combined information of the experimental data in the region of resolved resonances and in the continuum. The consequences of this analysis for the s-process component of the Os-187 abundance and the related impact on the evaluation of the time duration of galactic nucleosynthesis via the Re/Os cosmochronometer are discussed.
- Published
- 2010
35. TheZr92(n,γ) reaction and its implications for stellar nucleosynthesis
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D. Villamarin, J. Andrzejewski, Marco T. Pigni, Rene Reifarth, Carlo Rubbia, V. Vlachoudis, E. Jericha, J. Marganiec, S. Andriamonje, I. Savvidis, P. Pavlopoulos, L. Tavora, J. M. Quesada, E. Kossionides, F. Bečvář, P. F. Mastinu, M. Calviani, J. Pancin, P. Rullhusen, E. Chiaveri, D. Cano-Ott, Javier Praena, F. Gunsing, F. Alvarez-Velarde, S. David, G. Tagliente, M. C. Vincente, M. Kerveno, Gerald Badurek, Alfredo Ferrari, R. Ferreira-Marques, G. Cortes, L. Sarchiapone, Sara Bisterzo, C. Eleftheriadis, P. Cennini, A. Herrera-Martinez, N. Patronis, P. M. Milazzo, M. Krtička, F. Calviño, J. Cox, R. Gallino, Yacine Kadi, Alberto Mengoni, T. Martinez, R. C. Haight, D. Karamanis, U. Abbondanno, Laurent Tassan-Got, Michael Heil, M. Mosconi, M. Igashira, L. Perrot, L. Audouin, C. Stephan, S. O'Brien, J. Salgado, A. Poch, C. Santos, B. Haas, C. T. Papadopoulos, Michael Wiescher, R. Terlizzi, R. Vlastou, C. Pretel, E. Berthoumieux, E. Gonzalez-Romero, H. Leeb, A. Plukis, W. Dridi, F. Gramegna, Roberto Capote, Ralf Plag, I. Goncalves, S. Walter, I. Duran, F. Neves, Thomas Rauscher, K. Wisshak, C. Moreau, F. Käppeler, C. Carrapiço, S. Marrone, C. Massimi, G. Vannini, V. Chepel, C. Paradela, K. Fujii, S. Lukic, P. Baumann, H. Álvarez, C. Lamboudis, J. L. Tain, D. Karadimos, H. Wendler, Fabio Belloni, F. Voss, Carlos Guerrero, Heinz Oberhummer, Nicola Colonna, W.I. Furman, A. Lindote, C. A. Papachristodoulou, A. J. M. Plompen, M. Rosetti, G. Rudolf, I. Lopes, G. Aerts, I. Dillmann, A. Pavlik, C. Domingo-Pardo, M. Dahlfors, P. Vaz, Alberto Ventura, Aaron Couture, M. Embid-Segura, and Manuel Lozano
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Physics ,Nuclear reaction ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,7. Clean energy ,01 natural sciences ,Neutron temperature ,Nuclear physics ,Neutron capture ,Stellar nucleosynthesis ,Nucleosynthesis ,0103 physical sciences ,Isotopes of zirconium ,Neutron ,Nuclear Experiment ,s-process ,010303 astronomy & astrophysics - Abstract
Because the relatively small neutron capture cross sections of the zirconium isotopes are difficult to measure, the results of previous measurements are often not adequate for a number of problems in astrophysics and nuclear technology. Therefore, the Zr-92(n,gamma) cross section has been remeasured at the CERN n_TOF facility, providing a set of improved parameters for 44 resonances in the neutron energy range up to 40 keV. With this information the cross-section uncertainties in the keV region could be reduced to 5% as required for s-process nucleosynthesis studies and technological applications.
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- 2010
36. s-Process in Low Metallicity Stars. I. Theoretical Predictions
- Author
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Sergio Cristallo, Sara Bisterzo, R. Gallino, Oscar Straniero, and F. Kaeppeler
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Physics ,Red giant ,Metallicity ,White dwarf ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Stars ,Abundance of the chemical elements ,Carbon ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Nucleosynthesis ,AGB ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,s-process ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,Population II - Abstract
A large sample of carbon-enhanced metal-poor stars enriched in s-process elements (CEMP-s) have been observed in the Galactic halo. These stars of low mass (M∼ 0.9 M⊙) are located on the main-sequence or the red-giant phase, and do not undergo third dredge-up (TDU) episodes. The s-process enhancement is most plausibly due to accretion in a binary system from a more massive companion when on the asymptotic giant branch (AGB) phase (now a white dwarf). In order to interpret the spectroscopic observations, updated AGB models are needed to follow in detail the s-process nucleosynthesis. We present nucleosynthesis calculations based on AGB stellar models obtained with Frascati Raphson-Newton Evolutionary Code (FRANEC) for low initial stellar masses and low metallicities. For a given metallicity, a wide spread in the abundance of the s-process elements is obtained by varying the amount of 13C and its profile in the pocket, where the 13C(α, n)16O reaction is the major neutron source, releasing neutrons in radiative conditions during the interpulse phase. We also account for the second neutron source 22Ne(α, n)25Mg, partially activated during convective thermal pulses. We discuss the surface abundance of elements from carbon to bismuth, for AGB models of initial masses M= 1.3–2 M⊙, low metallicities ([Fe/H] from −1 down to −3.6) and for different 13C-pocket efficiencies. In particular, we analyse the relative behaviour of the three s-process peaks: light-s (ls at magic neutron number N= 50), heavy-s (hs at N= 82) and lead (N= 126). Two s-process indicators, [hs/ls] and [Pb/hs], are needed in order to characterize the s-process distribution. In the on-line material, we provide a set of data tables with surface predictions. Our final objective is to provide a full set of theoretical models of low-mass low-metallicity s-process-enhanced stars. In a forthcoming paper, we will test our results through a comparison with observations of CEMP-s stars., This work was supported by the Italian MIUR-PRIN 2006 Project ‘Late Phases of Stellar Evolution: Nucleosynthesis in Supernovae, AGB Stars, Planetary Nebulae’.
- Published
- 2010
37. Astrophysics at n-TOF facility at CERN
- Author
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G. Vannini, L. Perrot, Alfredo Ferrari, R. Ferreira-Marques, J. Salgado, A. Poch, P. E. Koehler, I. Goncalves, L. Tavora, Ralf Plag, Thomas Rauscher, M. Embid-Segura, E. Jericha, R. Vlastou, I. Duran, Sara Bisterzo, M. Kerveno, M. Krtička, F. Calviño, A. Herrera-Martinez, N. Patronis, C. Santos, E. Kossionides, Manuel Lozano, D. Karadimos, C. Pretel, W.I. Furman, V. Chepel, P. Rullhusen, J. Cox, T. Martinez, Javier Praena, F. Bečvář, Rene Reifarth, P. Baumann, I. Dillman, G. Aerts, Masayuki Igashira, Laurent Tassan-Got, A. Lindote, S. David, K. Fujii, Marco Calviani, P. Pavlopoulos, G. Cortes, G. Tagliente, P. Cennini, J. M. Quesada, S. Walter, A. J. M. Plompen, R. Gallino, C. Carrapiço, C Papadopoulos, E. Berthoumieux, Alberto Mengoni, G. Rudolf, I. Lopes, M. Mosconi, E. Gonzalez-Romero, Fabio Belloni, B. Haas, P. M. Milazzo, Michael Heil, F. Alvarez-Velarde, C. Stephan, L. Sarchiapone, Roberto Capote, R. Terlizzi, Gerald Badurek, A. Plukis, F. Neves, W. Dridi, Carlos Guerrero, D. Karamanis, S. Marrone, F. Gramegna, H. Álvarez, Heinz Oberhummer, J. L. Tain, J. Marganiec, S. Andriamonje, I. Savvidis, J. Andrzejewski, Carlo Rubbia, V. Vlachoudis, P. F. Mastinu, M. C. Vincente, C. Papachristodoulou, U. Abbondanno, J. Pancin, E. Chiaveri, D. Cano-Ott, R. C. Haight, M. Dahlfors, L. Audouin, Michael Wiescher, P. Vaz, D. Villamarin, Marco T. Pigni, Alberto Ventura, Aaron Couture, A. Pavlik, C. Domingo-Pardo, C. Eleftheriadis, C. Paradela, S. Lukic, Yacine Kadi, F. Käppeler, F. Voss, Nicola Colonna, H. Leeb, K. Wisshak, H. Wendler, F. Gunsing, Cristian Massimi, Universitat Politècnica de Catalunya. Departament de Física, Universitat Politècnica de Catalunya. ANT - Advanced Nuclear Technologies Research Group, G Tagliente, U Abbondanno, G Aert, H Alvarez, F Alvarez-Velarde, S Andriamonje, J Andrzejewski, L Audouin, G Badurek, P Baumann, F Bečvář, F Belloni, E Berthoumieux, S Bisterzo, F Calviño, M Calviani, D Cano-Ott, R Capote, C Carrapiço, P Cennini, V Chepel, E Chiaveri, N Colonna, G Corte, A Couture, J Cox, M Dahlfor, S David, I Dillman, C Domingo-Pardo, W Dridi, I Duran, C Eleftheriadi, M Embid-Segura, A Ferrari, R Ferreira-Marque, K Fujii, W Furman, R Gallino, I Goncalve, E Gonzalez-Romero, F Gramegna, C Guerrero, F Gunsing, B Haa, R Haight, M Heil, A Herrera-Martinez, M Igashira, E Jericha, F Käppeler, Y Kadi, D Karadimo, D Karamani, M Kerveno, P Koehler, E Kossionide, M Krtička, H Leeb, A Lindote, I Lope, M Lozano, S Lukic, J Marganiec, S Marrone, T Martinez, C Massimi, P Mastinu, A Mengoni, P M Milazzo, M Mosconi, F Neve, H Oberhummer, J Pancin, C Papachristodoulou, C Papadopoulo, C Paradela, N Patroni, A Pavlik, P Pavlopoulo, L Perrot, M T Pigni, R Plag, A Plompen, A Pluki, A Poch, J Praena, C Pretel, J Quesada, T Rauscher, R Reifarth, C Rubbia, G Rudolf, P Rullhusen, J Salgado, C Santo, L Sarchiapone, I Savvidi, C Stephan, J L Tain, L Tassan-Got, L Tavora, R Terlizzi, G Vannini, P Vaz, A Ventura, D Villamarin, M C Vincente, V Vlachoudi, R Vlastou, F Vo, S Walter, H Wendler, M Wiescher, and K Wisshak
- Subjects
s proce ,Nuclear reaction ,History ,Physics::Instrumentation and Detectors ,Astrophysics::High Energy Astrophysical Phenomena ,Nuclear Theory ,Nuclear physics ,Astrophysics ,Education ,CERN ,Neutron cross section ,Nuclear astrophysics ,Neutron ,Spallation ,n_TOF ,Nuclear Experiment ,Physics ,Neutrons ,Energies::Energia nuclear [Àrees temàtiques de la UPC] ,Física [Àrees temàtiques de la UPC] ,nucleosynthesis ,Computer Science Applications ,Neutron source ,Physics::Accelerator Physics ,Física nuclear ,s-process ,Nucleosynthesis ,Spallation Neutron Source - Abstract
The neutron time of flight (n_TOF) facility at CERN is a spallation neutron source with white neutron energy spectrum (from thermal to several GeV), covering the full energy range of interest for nuclear astrophysics, in particular for measurements of the neutron capture cross section required in s-process nucleosynthesis. This contribution presents an overview on the astrophysical program carried on at the n_TOF facility, the main results and their implications.
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- 2010
38. The effect of r-process enhancement in binary CEMP-s/r stars
- Author
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Roberto Gallino and Sara Bisterzo
- Subjects
Physics ,Supernova ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Nucleosynthesis ,Molecular cloud ,r-process ,White dwarf ,FOS: Physical sciences ,Binary system ,Astrophysics ,Low Mass ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
About half of carbon and s-process enhanced metal-poor stars (CEMP-s) show a high r-process enrichment (CEMP-s/r), incompatible with a pure s-process contribution. CEMP-s stars are of low mass (M < 0.9 Msun) and belong to binary systems. The C and s-process enrichment results from mass transfer by the winds of the primary AGB companion (now a white dwarf). The nucleosynthesis of the r-process, instead, is believed to occur in massive stars exploding as Supernovae of Type II. The most representative r-process element is Eu (95% of solar Eu). We suggest that the r-process enrichment was already present by local SNII pollution in the molecular cloud from which the binary system formed. The initial r-enrichment does not affect the s-process nucleosynthesis. However, the s-process indicators [hs/ls] (where ls is defined as the average of Y and Zr; hs as the average of La, Nd, Sm) and [Pb/hs] may depend on the initial r-enhancement. For instance, the hs-peak has to account of an r-process contribution estimated to be 30% for solar La, 40% for solar Nd, and 70% for solar Sm. A large spread of [Eu/Fe] is observed in unevolved halo stars up to [Eu/Fe] ~ 2. In presence of a very high initial r-enrichment of the molecular cloud, the maximum [hs/Fe] predicted in CEMP-s/r stars may increase up to 0.3 dex. Instead, the spread of [Y,Zr/Fe] observed in unevolved halo stars reaches a maximum of only ~ 0.5 dex, not affecting much the predicted [ls/Fe]. This is in agreement with observations of CEMP-s/r stars that show an observed [hs/ls] in average higher than that observed in CEMP-s. Preliminary results are presented., 5 pages, 4 figures
- Published
- 2010
- Full Text
- View/download PDF
39. Galactic Chemical Evolution of the s Process from AGB Stars
- Author
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Alessandra Serminato, Sara Bisterzo, Oscar Straniero, Roberto Gallino, and Claudia Travaglio
- Subjects
Physics ,Solar System ,Isotope ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Galaxy ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Asymptotic giant branch ,r-process ,Formation and evolution of the Solar System ,s-process ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
We follow the chemical evolution of the Galaxy for the s elements using a Galactic chemical evolution (GCE) model, as already discussed by Travaglio et al. (1999, 2001, 2004), with a full updated network and refined asymptotic giant branch (AGB) models. Calculations of the s contribution to each isotope at the epoch of the formation of the solar system is determined by following the GCE contribution by AGB stars only. Then, using the r-process residual method we determine for each isotope their solar system r-process fraction, and recalculate the GCE contribution of heavy elements accounting for both the s and r process. We compare our results with spectroscopic abundances at various metallicities of [Sr,Y,Zr/Fe], of [Ba,La/Fe], of [Pb/Fe], typical of the three s-process peaks, as well as of [Eu/Fe], which in turn is a typical r-process element. Analysis of the various uncertainties involved in these calculations are discussed., 8 pages, 6 figures, 1 table
- Published
- 2009
40. Barium Stars: Theoretical Interpretation
- Author
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Sara Bisterzo, Oscar Straniero, Roberto Gallino, L. Husti, and Sergio Cristallo
- Subjects
Physics ,Barium star ,White dwarf ,chemistry.chemical_element ,FOS: Physical sciences ,Astronomy and Astrophysics ,Barium ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Orbital period ,Spectral line ,Stars ,chemistry ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Nucleosynthesis ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics - Abstract
Barium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present the s-enhancement characteristic for AGB and post-AGB stars, but are in an earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They are believed to form in binary systems, where a more massive companion evolved faster, produced the s-elements during its AGB phase, polluted the present barium star through stellar winds and became a white dwarf. The samples of barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are analysed here. Spectra of both samples were obtained at high-resolution and high S/N. We compare these observations with AGB nucleosynthesis models using different initial masses and a spread of 13C-pocket efficiencies. Once a consistent solution is found for the whole elemental distribution of abundances, a proper dilution factor is applied. This dilution is explained by the fact that the s-rich material transferred from the AGB to the nowadays observed stars is mixed with the envelope of the accretor. We also analyse the mass transfer process, and obtain the wind velocity for giants and subgiants with known orbital period. We find evidence that thermohaline mixing is acting inside main sequence dwarfs and we present a method for estimating its depth., 8 pages, 11 figures, 6 tables
- Published
- 2009
41. Interpretation of CEMP(s) and CEMP(s + r) Stars with AGB Models
- Author
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Sara Bisterzo, Oscar Straniero, Wako Aoki, and Roberto Gallino
- Subjects
Physics ,Active galactic nucleus ,Milky Way ,Molecular cloud ,FOS: Physical sciences ,Astronomy and Astrophysics ,Quasar ,Astrophysics ,Galaxy ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Nucleosynthesis ,Asymptotic giant branch ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
Asymptotic Giant Branch (AGB) stars play a fundamental role in the s-process nucleosynthesis during their thermal pulsing phase. The theoretical predictions obtained by AGB models at different masses, s-process efficiencies, dilution factors and initial r-enrichment, are compared with spectroscopic observations of Carbon-Enhanced Metal-Poor stars enriched in s-process elements, CEMP(s), collected from the literature. We discuss here five stars as example, CS 22880-074, CS 22942-019, CS 29526-110, HE 0202-2204, and LP 625-44. All these objects lie on the main-sequence or on the giant phase, clearly before the TP-AGB stage: the hypothesis of mass transfer from an AGB companion, would explain the observed s-process enhancement. CS 29526-110 and LP 625-44 are CEMP(s+r) objects, and are interpreted assuming that the molecular cloud, from which the binary system formed, was already enriched in r-process elements by SNII pollution. In several cases, the observed s-process distribution may be accounted for AGB models of different initial masses with proper 13C-pocket efficiency and dilution factor. Na (and Mg), produced via the neutron capture chain starting from 22Ne, may provide an indicator of the initial AGB mass., 8 pages, 6 figures, 2 tables
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- 2009
42. Models and observations of the s process in AGB stars
- Author
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Sara Bisterzo, Amanda I. Karakas, and Maria Lugaro
- Subjects
Physics ,Stars ,Astrophysics ,s-process - Published
- 2009
43. Properties of the5−state at 839 keV inLu176and thes-process branching atA=176
- Author
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Sara Bisterzo, F. Käppeler, R. Gallino, Nicolas Winckler, Peter Mohr, and U. Kneissl
- Subjects
Mass number ,Physics ,Nuclear and High Energy Physics ,Branching fraction ,Intermediate state ,Atomic physics ,Branching (polymer chemistry) ,s-process ,Ground state ,Transition rate matrix ,Order of magnitude - Abstract
The s-process branching at mass number A=176 depends on the coupling between the high-K ground state and a low-lying low-K isomer in {sup 176}Lu. This coupling is based on electromagnetic transitions via intermediate states at higher energies. The properties of the lowest experimentally confirmed intermediate state at 839 keV are reviewed, and the transition rate between low-K and high-K states under stellar conditions is calculated on the basis of new experimental data for the 839-keV state. Properties of further candidates for intermediate states are briefly analyzed. It is found that the coupling between the high-K ground state and the low-K isomer in {sup 176}Lu is at least one order of magnitude stronger than previously assumed, leading to crucial consequences for the interpretation of the {sup 176}Lu/{sup 176}Hf pair as an s-process thermometer.
- Published
- 2009
44. Time scales of the s process - from minutes to ages
- Author
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Rene Reifarth, Sara Bisterzo, Marco Pignatari, R. Gallino, F. Käppeler, Oscar Straniero, K. Wisshak, Michael Heil, Nicolas Winckler, and S. Walter
- Subjects
Physics ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Astronomy ,FOS: Physical sciences ,Astronomy and Astrophysics ,Solar physics ,law.invention ,Astrophysics - Solar and Stellar Astrophysics ,Marine chronometer ,Space and Planetary Science ,law ,Space Science ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
A discussion of the time scales in the s process appears to be an approriate aspect to discuss at the occasion of 70th anniversary of Roberto Gallino, the more as this subject has been repeatedly addressed during the 20 years of collaboration between Torino and Karlsruhe. The two chronometers presented in this text were selected to illustrate the intense mutual stimulation of both groups. Based on a reliable set of accurate stellar (n, gamma) cross sections determined mostly at FZK, the Torino group succeeded to develop a comprehensive picture of the various s-process scenarios, which are most valuable for understanding the composition of the solar system as well as for the interpretation of an increasing number of astronomical observations., Comment: 8 pages, 5 figures
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- 2009
- Full Text
- View/download PDF
45. Stellar (n, γ) cross sections for Br and Rb: Matching the weak and mains-process components
- Author
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Sara Bisterzo, R. Gallino, Michael Heil, Ethan Uberseder, F. Käppeler, and Marco Pignatari
- Subjects
Nuclear reaction ,Physics ,Nuclear and High Energy Physics ,Stars ,Branching fraction ,Nucleosynthesis ,Gamma ray ,Asymptotic giant branch ,Neutron ,Atomic physics ,s-process - Abstract
The stellar (n, {gamma}) cross sections of {sup 79}Br, {sup 81}Br, {sup 85}Rb, and {sup 87}Rb have been determined by a series of ten activation measurements in a quasistellar neutron spectrum corresponding to a thermal energy of kT = 25 keV. The final uncertainties between 3 and 10% were dominated by the {gamma}-ray intensities in the decay of the respective reaction products. All other uncertainties were significantly reduced through variation of the experimental parameters. The consequences of these results for s-process nucleosynthesis of Br and Rb, and in particular of the local s-only isotopes {sup 80,} {sup 82}Kr and {sup 86,} {sup 87}Sr, are discussed with respect to the branching points at {sup 79}Se and {sup 85}Kr. The contributions of both the main s component from thermally pulsing low mass asymptotic giant branch stars and the weak s component from massive stars are considered in this analysis.
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- 2008
46. CS 22964-161: A Double-lined Carbon- and s-Process-enhanced Metal-poor Binary Star
- Author
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Sara Bisterzo, Stephen A. Shectman, G. S. Burley, Christopher Sneden, Roberto Gallino, Ian B. Thompson, George W. Preston, Inese I. Ivans, Sylvie Vauclair, Canadian Forest Service Great Lakes Forestry Centre (NRC), Natural Resources Canada (NRCan), Laboratoire Astrophysique de Toulouse-Tarbes (LATT), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), and Université Fédérale Toulouse Midi-Pyrénées
- Subjects
Metallicity ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Star (graph theory) ,01 natural sciences ,7. Clean energy ,Galactic halo ,Diffusion ,[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO] ,Primary (astronomy) ,Nucleosynthesis ,0103 physical sciences ,Binary star ,Nuclear Reactions ,Astrophysics::Solar and Stellar Astrophysics ,Abundances ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Physics ,010308 nuclear & particles physics ,Astrophysics (astro-ph) ,Stars: Binaries: Spectroscopic ,Astronomy and Astrophysics ,Stars: Abundances ,stars: individual (CS 22964-161) ,Stars ,13. Climate action ,Space and Planetary Science ,Stars: Population II ,Astrophysics::Earth and Planetary Astrophysics ,s-process - Abstract
A detailed high-resolution spectroscopic analysis is presented for the carbon-rich low metallicity Galactic halo object CS 22964-161. We have discovered that CS 22964-161 is a double-lined spectroscopic binary, and have derived accurate orbital components for the system. From a model atmosphere analysis we show that both components are near the metal-poor main-sequence turnoff. Both stars are very enriched in carbon and in neutron-capture elements that can be created in the s-process, including lead. The primary star also possesses an abundance of lithium close to the value of the ``Spite-Plateau''. The simplest interpretation is that the binary members seen today were the recipients of these anomalous abundances from a third star that was losing mass as part of its AGB evolution. We compare the observed CS 22964-161 abundance set with nucleosynthesis predictions of AGB stars, and discuss issues of envelope stability in the observed stars under mass transfer conditions, and consider the dynamical stability of the alleged original triple star. Finally, we consider the circumstances that permit survival of lithium, whatever its origin, in the spectrum of this extraordinary system., manuscript, 7 tables, 13 figures. ApJ, in press
- Published
- 2008
47. Neutron capture cross section ofZr90: Bottleneck in thes-process reaction flow
- Author
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L. Ferrant, W.I. Furman, Corrie S. Moreau, I. Duran, L. Tavora, C. A. Papachristodoulou, J. Pancin, J. Salgado, K. Fujii, A. Poch, G. Cortes, G. Aerts, P. Rullhusen, Carlos Guerrero, U. Abbondanno, A. J. M. Plompen, Heinz Oberhummer, S. Walter, V. Chepel, G. Rudolf, Ralf Plag, C. Carrapiço, F. Voss, I. Lopes, Sara Bisterzo, F. Becvar, M. C. Vincente, Y. Kadi, H. Leeb, M. Embid-Segura, P. Baumann, E. Kossionides, Roberto Capote, Christoph A. Stephan, C. Santos, S. David, C. Eleftheriadis, P.A. Assimakopoulos, P. Cennini, James L. Cox, F. Neves, J. Andrzejewski, P. M. Milazzo, A. Pavlik, G. Tagliente, A. Herrera-Martinez, N. Patronis, Javier Praena, C. Domingo-Pardo, I. Dillman, Manuel Lozano, Vasilis Vlachoudis, Arnaud Ferrari, M. Mosconi, Thomas Rauscher, K. Wisshak, E. Jericha, Marco Calviani, D. Karamanis, S. O'Brien, L. Perrot, C. Pretel, A. Lindote, S. Lukic, R. Terlizzi, D. Karadimos, P. E. Koehler, H. Wendler, P. Pavlopoulos, F. Alvarez-Velarde, F. Gunsing, Gerald Badurek, M. Dahlfors, A. Mengoni, L. Sarchiapone, F. Gramegna, Cristian Massimi, P. Vaz, R. Vlastou, Aaron Couture, D. Cano-Ott, E. Berthoumieux, R. Gallino, Michael Heil, I. Savvidis, Masayuki Igashira, F. Kaeppeler, B. Haas, W. Dridi, Rene Reifarth, N. Colonna, J. M. Quesada, L. Tassan-Got, A. Ventura, E. Gonzalez-Romero, A. Plukis, D. Villamarin, Marco T. Pigni, M. Krtička, F. Calviño, R. Ferreira-Marques, T. Martinez, R. C. Haight, C. Paradela, J. Marganiec, S. Andriamonje, E. Chiaveri, L. Audouin, P. F. Mastinu, Michael Wiescher, H. Álvarez, C. Lamboudis, J. L. Tain, M. Kerveno, C. T. Papadopoulos, C. Rubbia, Isabel S. Gonçalves, S. Marrone, and G. Vannini
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Nuclear reaction ,Physics ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Nuclear Theory ,7. Clean energy ,01 natural sciences ,Neutron temperature ,Nuclear physics ,Neutron capture ,0103 physical sciences ,Neutron cross section ,Neutron source ,Neutron ,Nuclear Experiment ,s-process ,010303 astronomy & astrophysics ,Spallation Neutron Source - Abstract
The neutron capture cross sections of the Zr isotopes have important implications in nuclear astrophysics and for reactor design. The small cross section of the neutron magic nucleus Zr-90, which accounts for more than 50 for the stellar s-process, because it acts as a bottleneck in the neutron capture chain between the Fe seed and the heavier isotopes. The same element, Zr, also is an important component of the structural materials used in traditional and advanced nuclear reactors. The (n, gamma) cross section has been measured at CERN, using the n_TOF spallation neutron source. In total, 45 resonances could be resolved in the neutron energy range below 70 keV, 10 being observed for the first time thanks to the high resolution and low backgrounds at n_TOF. On average, the Gamma(gamma) widths obtained in resonance analyses with the R-matrix code SAMMY were 15 these results, the accuracy of the Maxwellian averaged cross section for s-process calculations has been improved by more than a factor of 2.
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- 2008
48. The Lithium-, r- and s-Enhanced Metal-Poor Giant HK-II 17435-00532
- Author
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Ian U. Roederer, Anna Frebel, Matthew Shetrone, Carlos Allende Prieto, Jaehyon Rhee, Roberto Gallino, Sara Bisterzo, Christopher Sneden, Timothy C. Beers, John J. Cowan, Roald Guandalini, Sara Palmerini, and Maurizio Busso
- Subjects
Physics ,Red-giant branch ,chemistry ,Nucleosynthesis ,Analytical chemistry ,Asymptotic giant branch ,chemistry.chemical_element ,Lithium ,Astrophysics ,Horizontal branch ,s-process ,Stellar evolution ,Abundance of the chemical elements - Abstract
We present the first detailed abundance analysis of the metal‐poor giant HK‐II 17435‐00532. This star was observed as part of the University of Texas Long‐Term Chemical Abundances of Stars in the Halo (CASH) Project. A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby‐Eberly Telescope with a resolving power of R∼15000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal‐poor ([Fe/H] = −2.2) star has an unusually high lithium abundance (loge(Li) = +2.1), mild carbon ([C/Fe] = +0.7) and sodium ([Na/Fe] = +0.6) enhancement, as well as enhancement of both s‐process ([Ba/Fe] = +0.8) and r‐process ([Eu/Fe] = +0.5) material. The high Li abundance can be explained by self‐enrichment through extra mixing mechanisms that connect the convective envelope with the outer regions of the H‐burning shell. If so, HK‐II 17435‐00532 is the most metal‐poor starin which this short‐lived phase of...
- Published
- 2008
49. The measurement of the 206Pbn, gamma cross section and stellar implications
- Author
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L. Tavora, L. Perrot, I. Savvidis, E. Gonzalez-Romero, P. Rullhusen, A. Plukis, F. Käppeler, R. Ferreira-Marques, L. Ferrant, R. C. Haight, D. Karamanis, I. Dillmann, P. Pavlopoulos, C. Paradela, I. Duran, M. C. Vincente, V. Chepel, Rene Reifarth, J. M. Quesada, L. Tassan-Got, L. Audouin, P. Baumann, B. Haas, Michael Wiescher, J. Andrzejewski, G. Aerts, C. Carrapiço, A. J. M. Plompen, U. Abbondanno, P. E. Koehler, Carlo Rubbia, W. Dridi, W.I. Furman, M. Dahlfors, G. Rudolf, I. Lopes, D. Villamarin, Marco T. Pigni, James L. Cox, F. Bečvář, E. Berthoumieux, P. Vaz, C. A. Papachristodoulou, F. Neves, P. M. Milazzo, Alberto Ventura, Aaron Couture, E. Jericha, S. Walter, S. Lukic, F. Gramegna, Ralf Plag, J. Salgado, A. Poch, J. Marganiec, S. Andriamonje, P. F. Mastinu, L. Sarchiapone, H. Leeb, Masayuki Igashira, J. Pancin, P. Cennini, Carlos Guerrero, F. Gunsing, M. Embid-Segura, G. Cortes, M. Mosconi, R. Vlastou, Heinz Oberhummer, C. Stephan, S. O'Brien, F. Voss, Manuel Lozano, Y. Kadi, Cristian Massimi, R. Terlizzi, M. Krtička, F. Calviño, Marco Calviani, Nicola Colonna, Vasilis Vlachoudis, S. David, G. Tagliente, K. Wisshak, A. Pavlik, Roberto Capote, P.A. Assimakopoulos, C. Domingo-Pardo, G. Vannini, F. Alvarez-Velarde, D. Cano-Ott, Gerald Badurek, A. Lindote, C. T. Papadopoulos, S. Marrone, H. Álvarez, R. Gallino, C. Lamboudis, J. L. Tain, Michael Heil, M. Kerveno, E. Kossionides, C. Eleftheriadis, I. Goncalves, Thomas Rauscher, C. Santos, D. Karadimos, K. Fujii, C. Pretel, Sara Bisterzo, A. Herrera-Martinez, N. Patronis, Arnaud Ferrari, Alberto Mengoni, Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Département Recherches Subatomiques (DRS-IPHC), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Louis Pasteur - Strasbourg I-Centre National de la Recherche Scientifique (CNRS), Institut de Physique Nucléaire d'Orsay (IPNO), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre d'Etudes Nucléaires de Bordeaux Gradignan (CENBG), Université Sciences et Technologies - Bordeaux 1-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), nTOF, C Domingo-Pardo, U Abbondanno, G Aert, H Álvarez, F Alvarez-Velarde, S Andriamonje, J Andrzejewski, P Assimakopoulo, L Audouin, G Badurek, P Baumann, F Bečvář, E Berthoumieux, S Bisterzo, F Calviño, M Calviani, D Cano-Ott, R Capote, C Carrapiço, P Cennini, V Chepel, N Colonna, G Corte, A Couture, J Cox, M Dahlfor, S David, I Dillmann, W Dridi, I Duran, C Eleftheriadi, M Embid-Segura, L Ferrant, A Ferrari, R Ferreira-Marque, K Fujii, W Furman, R Gallino, I Goncalve, E Gonzalez-Romero, F Gramegna, C Guerrero, F Gunsing, B Haa, R Haight, M Heil, A Herrera-Martinez, M Igashira, E Jericha, Y Kadi, F Käppeler, D Karadimo, D Karamani, M Kerveno, P Koehler, E Kossionide, M Krtička, C Lamboudi, H Leeb, A Lindote, I Lope, M Lozano, S Lukic, J Marganiec, S Marrone, C Massimi, P Mastinu, A Mengoni, P M Milazzo, M Mosconi, F Neve, H Oberhummer, S O'Brien, J Pancin, C Papachristodoulou, C Papadopoulo, C Paradela, N Patroni, A Pavlik, P Pavlopoulo, L Perrot, M T Pigni, R Plag, A Plompen, A Pluki, A Poch, C Pretel, J Quesada, T Rauscher, R Reifarth, C Rubbia, G Rudolf, P Rullhusen, J Salgado, C Santo, L Sarchiapone, I Savvidi, C Stephan, G Tagliente, J L Tain, L Tassan-Got, L Tavora, R Terlizzi, G Vannini, P Vaz, A Ventura, D Villamarin, M C Vincente, V Vlachoudi, R Vlastou, F Vo, S Walter, M Wiescher, K Wisshak, and Université Sciences et Technologies - Bordeaux 1 (UB)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Physics ,s proce ,Nuclear and High Energy Physics ,Spectrometer ,experiment ,[PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex] ,01 natural sciences ,7. Clean energy ,Nuclear physics ,Cross section (physics) ,Neutron capture ,Stellar nucleosynthesis ,13. Climate action ,Nucleosynthesis ,0103 physical sciences ,Neutron cross section ,r-process ,CERN n_TOF spectrometer ,Alpha decay ,010306 general physics ,010303 astronomy & astrophysics - Abstract
The neutron capture cross section of (206)Pb has been measured at the CERN n_TOF spectrometer using a setup of two C(6)D(6) detectors. In the energy interval from 1 eV to 600 keV the cross section is dominated by resonances, which were analyzed via the R-matrix analysis code SAMMY. In the relevant energy ranges for stellar nucleosynthesis, i. e., at thermal energies of kT = 8 keV and kT = 23 keV, the present Maxwellian average cross section differs by 20% and 9% from the recommended values of Bao et al respectively. From the new cross section the s-abundance of (206)Pb could be reliably determined as 70( 4)%. This result is of importance in order to test and constrain r-process abundance calculations in the actinide region, because the r-process portion of (206)Pb is dominated by alpha-back decays of short-lived transbismuth isotopes.
- Published
- 2008
50. CEMP–s Stars: AGB Yield Predictions and Thermohaline Mixing
- Author
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R. Gallino, Sara Bisterzo, G. W. Preston, W. Aoki, Inese I. Ivans, and Oscar Straniero
- Subjects
Physics ,Stars ,Convection zone ,Nucleosynthesis ,Binary star ,Asymptotic giant branch ,Astronomy ,Thermohaline circulation ,Astrophysics ,Dredge-up ,Stellar evolution - Abstract
CS 29497–030 and CS 31062–050 belong to a sample of C‐rich, s‐process rich and extremely metal‐poor stars (CEMP–s+r). To explain the s–process enrichment, we considered these stars to be extrinsic asymptotic giant branch (AGB) stars, belonging to binary systems where the more massive AGB companion polluted the observed star (of ∼0.8 M⊙) with efficient stellar winds. To explain the r–process enrichment, we assumed that the parental cloud was already enriched in r‐process elements.For the main sequence CS 29497–030 we hypothesize that the primary AGB had an initial mass of ∼1.3 M⊙ and underwent a very limited number of third dredge up episodes. A very small dilution between AGB winds and envelope mass of the observed star is derived by comparing AGB nucleosynthesis yields and observed abundances, consistent with the fact that dwarf stars of ∼0.8 M⊙ are characterized by a limited subphotospheric convective zone. This is compatible with moderate thermohaline mixing (e.g., [l]). AGB models of higher initial ma...
- Published
- 2008
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