Showing papers on "Stellar nucleosynthesis published in 2001"
TL;DR: In this paper, the authors studied the evolution of supernova-driven bubbles as they blow out from subgalactic halos and propagate into the intergalactic medium (IGM), and showed that to lift the halo gas out of the potential well, the energy injection must continue at least until blowaway occurs.
Abstract: We assess supernova-driven pregalactic outflows as a mechanism for distributing the product of stellar nucleosynthesis over large cosmological volumes prior to the reionization epoch. Supernova (SN) ejecta will escape the grasp of halos with virial temperatures Tvir 104.3 K (corresponding to masses M 108 h-1 M☉ at redshift z = 9 when they collapse from 2 σ fluctuations) if rapid cooling can take place, and a significant fraction of their baryonic mass is converted into stars over a dynamical timescale. We study the evolution of SN-driven bubbles as they blow out from subgalactic halos and propagate into the intergalactic medium (IGM), and we show that to lift the halo gas out of the potential well, the energy injection must continue at least until blowaway occurs. If the fraction of ionizing photons that escape the dense sites of star formation into intergalactic space is greater than a few percent, pregalactic outflows will propagate into an IGM that has been prephotoionized by the same massive stars that later explode as SNe, and the expansion of the metal-enriched bubbles will be halted by the combined action of external pressure, gravity, and radiative losses. The collective explosive output of about 10,000 SNe per M 108 h-1 M☉ halo at these early epochs could pollute vast regions of intergalactic space to a mean metallicity Z = ΩZ/Ωb 0.003 (comparable to the levels observed in the Lyα forest at z ≈ 3) without hydrodynamically perturbing the IGM much, i.e., producing large variations of the baryons relative to the dark matter. Rayleigh-Taylor instabilities between the dense shell that contains pristine swept-up material and the hot, metal-enriched, low-density bubble may contribute to the mixing and diffusion of heavy elements. The volume filling factor of the ejecta is higher than 20% if the star formation efficiency is on the order of 10%. Larger filling factors (not required by current observations) may be obtained for larger efficiencies, moderately top-heavy initial mass functions, halos for which a significant fraction of the gas is in a galactic disk and does not couple to the outflow (since matter is ejected perpendicularly to the disk), or from a population of more numerous sources—which would therefore have to originate from lower amplitude peaks. When the filling factor of the ejecta becomes significant, enriched material typically will be at a higher adiabat than expected from photoionization.
373 citations
TL;DR: In this paper, the role of light, neutron-rich nuclei during the r-process nucleosynthesis in supernovae was studied and a new nuclear reaction flow path opened in the very light, neutrinos-rich region.
Abstract: We study the role of light, neutron-rich nuclei during r-process nucleosynthesis in supernovae Most previous studies of the r-process have concentrated on the reaction flow of heavy, unstable nuclei Although the nuclear reaction network includes a few thousand heavy nuclei, only limited reaction flow through light nuclei near the stability line has been used in those studies However, in a viable scenario of the r-process in neutrino-driven winds, the initial condition is a high-entropy hot plasma consisting of neutrons, protons, and electron-positron pairs experiencing an intense flux of neutrinos In such environments, light nuclei, as well as heavy nuclei, are expected to play important roles in the production of seed nuclei and r-process elements Thus, we have extended our fully implicit nuclear reaction network so that it includes all nuclei up to the neutron-drip line for Z ≤ 10, in addition to a larger network for Z ≥ 10 In the present nucleosynthesis study, we utilize a wind model of massive Type II supernova explosions to study the effects of this extended network We find that a new nuclear reaction flow path opens in the very light, neutron-rich region This new nuclear reaction flow can change the final heavy-element abundances by as much as an order of magnitude
121 citations
TL;DR: In this paper, the authors developed a detailed standard chemi-cal evolution model to study the evolution of all the chemical elements up to the iron peak in the solar vicinity, and they considered that the Galaxy was formed through two episodes of exponentially decreasing infall, out of extragalactic gas.
Abstract: We have developed a detailed standard chemi- cal evolution model to study the evolution of all the chem- ical elements up to the iron peak in the solar vicinity. We consider that the Galaxy was formed through two episodes of exponentially decreasing infall, out of extragalactic gas. In a first infall episode, with a duration of ∼ 1 Gyr, the halo and the thick disk were assembled out of primordial gas, while the thin disk formed in a second episode of in- fall of slightly enriched extragalactic gas, with much longer timescale. The model nicely reproduces the main observa- tional constraints of the solar neighborhood, and the cal- culated elemental abundances at the time of the solar birth are in excellent agreement with the solar abundances. By the inclusion of metallicity dependent yields for the whole range of stellar masses we follow the evolution of 76 iso- topes of all the chemical elements between hydrogen and zinc. Those results are confronted with a large and recent body of observational data, and we discuss in detail the implications for stellar nucleosynthesis.
112 citations
TL;DR: In this paper, a model to implement metal enrichment in a cosmological context based on the hydrodynamical AP3MSPH code described by Tissera, Lambas and Abadi was developed.
Abstract: We develop a model to implement metal enrichment in a cosmological context based on the hydrodynamical AP3MSPH code described by Tissera, Lambas and Abadi (1997). The star formation model is based on the Schmidt law and has been modified in order to describe the transformation of gas into stars in more detail. The enrichment of the interstellar medium due to supernovae I and II explosions is taken into account by assuming a Salpeter Initial Mass Function and different nucleosynthesis models. The different chemical elements are mixed within the gaseous medium according to the Smooth Particle Hydrodynamics technique. Gas particles can be enriched by different neighbouring particles at the same time. We present tests of the code that assess the effects of resolution and model parameters on the results. We show that the main effect of low numerical resolution is to produce a more effective mixing of elements, resulting in abundance relations with less dispersion. We have performed cosmological simulations in a standard Cold Dark Matter scenario and we present results of the analysis of the star formation and chemical properties of the interstellar medium and stellar population of the simulated galactic objects. We show that these systems reproduce abundance ratios for primary and secondary elements of the interstellar medium, and the correlation between the (O/H) abundance and the gas fraction of galaxies. We find that star formation efficiency, the relative rate of supernovae II to supernovae I and life-time of binary systems as well as the stellar nucleosynthesis
93 citations
TL;DR: In this paper, a model was proposed to explain the stellar abundances of r-process elements and other elements associated with the R-process sites, and good agreement was obtained between the model results and data over the range -3 < [Fe/H] < -1.
Abstract: A model is presented that seeks to explain quantitatively the stellar abundances of r-process elements and other elements associated with the r-process sites. It is argued that the abundances of all these elements in stars with -3 ≾[Fe/H] 130) r-elements but no Fe (presumably leaving behind black holes). The L events are of low frequency and produce Fe and dominantly light (A ≾ 130) r-elements (essentially none above Ba). By using the observed abundances in two ultra-metal-poor stars and the solar r-abundances, the initial or prompt inventory of elements produced by the first generations of very massive stars and the yields of H and L events can be determined. The abundances of a large number of elements in a star can then be calculated from the model by using only the observed Eu and Fe abundances. To match the model results and the observational data for stars with -3 < [Fe/H] < -1 requires that the solar r-abundances for Sr, Y, Zr, and Ba must be significantly increased from the standard values. No such changes appear to be required for all other elements. If the changes in the solar r-abundances for Sr, Y, Zr, and Ba are not permitted, the model fails at -3 < [Fe/H] < -1 but still works at [Fe/H] ≈ -3 for these four elements. By using the corrected solar r-abundances for these elements, good agreement is obtained between the model results and data over the range -3 < [Fe/H] < -1. No evidence of s-process contributions is found in this region, but all the observational data in this region now show regular increases of Ba/Eu above the standard solar r-process value. Whether the solar r-components of Sr, Y, Zr, and Ba used here to obtain a fit to the stellar data can be reconciled with those obtained from solar abundances by subtracting the s-components calculated from models is not clear.
85 citations
TL;DR: In this paper, a broad range of nucleosynthesis scenarios from the Big Bang to the different conditions during stellar evolution and stellar explosion are discussed and the uncertainties are given for all of these scenarios.
Abstract: Nuclear Astrophysics is concerned with the study of nuclear processes at stellar temperature and density conditions. A main goal is the understanding of the synthesis of the elements and the generation of energy guiding stellar evolution and driving stellar explosions. Observables (like e.g. luminosity curves or elemental abundance distributions) witness the interplay between nuclear structure aspects near the particle drip-lines and the appropriate astrophysical environments, and give guidance to and constraints on stellar conditions and the associated nucleosynthesis. We present an overview of the broad range of nucleosynthesis scenarios from the Big Bang to the different conditions during stellar evolution and stellar explosion. Special emphasis is given to the discussion of nuclear physics aspects of pre-supernova collapse and supernova shock front nucleosynthesis. Of great interests are presently nucleosynthesis processes far from the limits of stability like the neutron diriven r-process and the hydrogen driven rp-process. The nuclear physics of the r-process and the possible site for the r-process in the neutrino driven wind of the supernova shock are discussed and the possible impact of neutrino induced processes is presented. Hydrogen induced explosive processes occur in the thermonuclear runaway on the surface of accreting compact stars at electron degenerate conditions. This includes novae triggered by accretion on white dwarfs and x-ray bursts initiated by accretion on neutron stars. High accretion rates on white dwarfs and neutron stars lead to supernova type Ia explosions or to x-ray pulsars respectively. An overview of the nucleosynthesis conditions and uncertainties is given for all of these scenarios.
79 citations
TL;DR: In this article, the authors show that the development of mixing episodes at the beginning of the AGB phase allows low-and intermediate-mass stars to experience thermal pulses, which leads to the production of s-process nuclei up to Pb and Bi.
Abstract: Contrary to previous expectations, recent evolutionary models of zero-metallicity stars show that the development of mixing episodes at the beginning of the AGB phase allows low- and intermediate-mass stars to experience thermal pulses. If these stars, like their metal-rich counterparts, also experience partial mixing of protons from the H-rich envelope into the C-rich layers at the time of the third dredge-up, an extensive neutron capture nucleosynthesis leads to the production of s-process nuclei up to Pb and Bi. Nucleosynthesis calculations based on stellar AGB models are performed assuming a parameterized H-abundance prole below the convective envelope at the time of the third dredge-up. Despite the absence of Fe-group elements, the large neutron flux resulting from the 13 C( ;n) 16 O reaction leads to an ecient production of s-process elements starting from the neutron captures on the C-Ne isotopes. Provided partial mixing of protons takes place, it is shown that population III AGB stars should be enriched in s-process elements and overall in Pb and Bi.
68 citations
TL;DR: In this article, the role of nuclear physics in astrophysics in general and in particular how it affects stellar events and the resulting nucleosynthesis is examined in a review of stellar modeling, and the main emphasis is put on the connection to element synthesis.
68 citations
TL;DR: In this paper, a relativistic hydrodynamic simulation of adiabatic collapse and bounce was performed to evaluate the products of r-process nucleosynthesis in the supernova ejecta.
Abstract: We reanalyze r-process nucleosynthesis in the neutron-rich ejecta from a prompt supernova explosion of a low-mass (11 M?) progenitor. Although it has not yet been established that a prompt explosion can occur, it is not yet ruled out as a possibility for low-mass supernova progenitors. Moreover, there is mounting evidence that a new r-process site may be required. Hence, we assume that a prompt explosion can occur and make a study of r-process nucleosynthesis in the supernova ejecta. To achieve a prompt explosion we have performed a general relativistic hydrodynamic simulation of adiabatic collapse and bounce using a relativistic nuclear-matter equation of state. The electron fraction Ye during the collapse was fixed at the initial-model value. The size of the inner collapsing core was then large enough to enable a prompt explosion to occur in the hydrodynamic calculation. Adopting the calculated trajectories of promptly ejected material, we explicitly computed the burst of neutronization due to electron captures on free protons in the photodissociated ejecta after the passage of the shock. The thermal and compositional evolution of the resulting neutron-rich ejecta originating from near the surface of the proto-neutron star was obtained. These were used in nuclear reaction network calculations to evaluate the products of r-process nucleosynthesis. We find that, unlike earlier studies of nucleosynthesis in prompt supernovae, the amount of r-process material ejected per supernova is quite consistent with observed Galactic r-process abundances. Furthermore, the computed r-process abundances are in good agreement with solar abundances of r-process elements for A > 100. This suggests that prompt supernovae are still viable r-process sites. Such events may be responsible for the abundances of the heaviest r-process nuclei.
66 citations
TL;DR: In this article, the authors explore the origin of carbon and calculate the abundance evolution of CNO elements for 8 dierent models of stellar nucleosynthesis yields using the standard infall model of Galactic chemical evolution.
Abstract: Using the standard infall model of Galactic chemical evolution, we explore the origin of carbon and calculate the abundance evolution of CNO elements for 8 dierent models of stellar nucleosynthesis yields. The results show that, in the early stage of the Galaxy, massive stars are the main producer of carbon, and that as our Galaxy evolves to the late stage, the longer lived intermediate- and low-mass stars play an increasingly important role, while at the same time, metal-rich Wolf-Rayet stars eject a signicant amount of carbon into the ISM by radiative-driven stellar winds. However, from the present published nucleosynthesis yields we cannot distinguish whether the main source of carbon in the late Galactic stage is just the massive stars ( M> 8 M) alone, or just the intermediate-, low-mass stars and M 40 M massive stars that do not go through the Wolf-Rayet stage. The 12 C(; ) 16 O reaction rate is very important in the stellar nucleosynthesis calculations: a lower rate will give a higher yield of carbon. The contribution to nitrogen is dominated by intermediate- and low-mass stars, and the secondary source of massive stars cannot explain the observed (N/Fe) in metal-poor stars. Most of oxygen is produced by massive stars. The fact that a higher O abundance in metal-poor stars is derived from the O i 7771 7775 A triplet than from the forbidden (O i) line at 6300 A poses a problem.
39 citations
TL;DR: In this article, the first detection of Cobalt in a Damped Lyman Alpha system (DLA) at z ~ 2 was reported. But the Co abundance in DLAs may also help to constrain models of stellar nucleosynthesis in a regime not probed by Galactic stars.
Abstract: We present the first ever detection of Cobalt in a Damped Lyman Alpha system (DLA) at z ~ 2. In addition to providing important clues to the star formation history of these high redshift galaxies, we discuss how studying the Co abundance in DLAs may also help to constrain models of stellar nucleosynthesis in a regime not probed by Galactic stars.
TL;DR: In this paper, the first detection of Cobalt in a Damped Lyman Alpha system (DLA) at z = 1.92 was reported, and the Co abundance in DLAs may also help to constrain models of stellar nucleosynthesis in a regime not probed by Galactic stars.
Abstract: We present the first ever detection of Cobalt in a Damped Lyman Alpha system (DLA) at z = 1.92. In addition to providing important clues to the star formation history of these high redshift galaxies, we discuss how studying the Co abundance in DLAs may also help to constrain models of stellar nucleosynthesis in a regime not probed by Galactic stars.
TL;DR: The origin of nucleosynthesis products of rapid neutron capture reactions (the r-process) is a longstanding astrophysical problem as discussed by the authors, and the abundance distributions of some extremely metal-poor stars with those of the best-observed supernova SN 1987A have been analyzed.
Abstract: The origin of nucleosynthesis products of rapid neutron capture reactions (the r-process) is a longstanding astrophysical problem. Recent analyses of elemental abundances for extremely metal-poor stars shed light on the elemental abundances of individual supernovae. Comparison of the abundance distributions of some extremely metal-poor stars with those of the best-observed supernova SN 1987A clearly indicates that the overabundances of barium and strontium found in SN 1987A that have been ascribed to the slow neutron capture process must be results of r-process nucleosynthesis. The mass of freshly synthesized barium in SN 1987A is estimated to be 6x10^-6 solar mass based on the observed surface abundance and detailed hydrodynamical models for this supernova. These new findings lead to the conclusion that 20 solar mass stars, one of which is the progenitor star of SN 1987A, are the predominant production sites for r-process elements in the Galaxy and the r-process element donors for notable neutron-capture-rich giant stars, CS22892-052 and CS31082-001.
TL;DR: In this article, the authors examined the features of a steady and subsonic wind solution which extend the model of Weber and Davis (1967), which is a representative solar wind model and found that the entropy per baryon becomes lower and the dynamical timescale becomes longer as the angular velocity becomes higher.
Abstract: We have studied whether the rotation and magnetic fields in neutrino-driven winds can be key processes for the rapid-process (r-process) nucleosynthesis. We have examined the features of a steady and subsonic wind solutions which extend the model of Weber and Davis (1967), which is a representative solar wind model. As a result, we found that the entropy per baryon becomes lower and the dynamical timescale becomes longer as the angular velocity becomes higher. These results are inappropriate for the production of the r-process nuclei. As for the effects of magnetic fields, we found that a solution as a steady wind from the surface of the proto-neutron star can not be obtained when the strength of the magnetic field becomes $\ge$ $10^{11}$ G. Since the magnetic field in normal pulsars is of order $10^{12}$ G, a steady wind solution might not be realized there, which means that the models in this study may not be adopted for normal proto-neutron stars. In this situation, we have little choice but to conclude that it is difficult to realize a successful r-process nucleosynthesis in the wind models in this framework.
TL;DR: In this article, the authors examined the features of a steady, subsonic, and rigidly rotating jet in which the centrifugal force is balanced by the magnetic force and found that the r-process does not occur because the final temperature is kept too high and the dynamical timescale becomes too long when the neutrino luminosities are set to be high.
Abstract: We have studied whether the jet in a collapse-driven supernova can be a key process for the rapid-process (r-process) nucleosynthesis. We have examined the features of a steady, subsonic, and rigidly rotating jet in which the centrifugal force is balanced by the magnetic force. As for the models in which the magnetic field is weak and angular velocity is small, we found that the r-process does not occur because the final temperature is kept too high and the dynamical timescale becomes too long when the neutrino luminosities are set to be high. Even if the luminosities of the neutrinos are set to be low, which results in the low final temperature, we found that the models do not give a required condition to produce the r-process matter. Furthermore, the amount of the mass outflow seems to be too little to explain the solar system abundance ratio in such low-luminosity models. As for the models in which the magnetic field is strong and angular velocity is large, we found that the entropy per baryon becomes too small and the dynamical timescale becomes too long. This tendency is, of course, a bad one for the production of the r-process nuclei. As a conclusion, we have to say that it is difficult to cause a successful r-process nucleosynthesis in the jet models in this study.
TL;DR: In this article, the acceptable range in Omega_b changes in the presence of antimatter regions, as compared to the standard big bang nucleosynthesis, and it is shown that it is possible to produce at the same time both a low 4He value (Y_p < 0.240) and a low D/H value (D/H < 4e-5), but overproduction of 7Li is unavoidable at large Omega-b.
Abstract: Production of regions of antimatter in the early universe is predicted in many baryogenesis models. Small scale antimatter regions would annihilate during or soon after nucleosynthesis, affecting the abundances of the light elements. In this paper we study how the acceptable range in Omega_b changes in the presence of antimatter regions, as compared to the standard big bang nucleosynthesis. It turns out that it is possible to produce at the same time both a low 4He value (Y_p < 0.240) and a low D/H value (D/H < 4e-5), but overproduction of 7Li is unavoidable at large Omega_b.
21 Nov 2001
TL;DR: In this paper, the authors attempt to compile some major issues in cosmochemistry that can be addressed with a better knowledge of the respective element or isotope abundances present and future missions such as Genesis, Stardust, Interstellar Pathfinder, and Interstellar Probe.
Abstract: Understanding the evolution of the universe from Big Bang to its present state requires an understanding of the evolution of the abundances of the elements and isotopes in galaxies, stars, the interstellar medium, the Sun and the
heliosphere, planets and meteorites Processes that change the state of the universe include Big Bang nucleosynthesis,
star formation and stellar nucleosynthesis, galactic chemical evolution, propagation of cosmic rays, spallation, ionization and particle transport of interstellar material, formation of the solar system, solar wind emission and its fractionation (FIP/FIT effect), mixing processes in stellar interiors, condensation of material and subsequent geochemical fractionation Here, we attempt to compile some major issues in cosmochemistry that can be addressed with a better knowledge of the respective element or isotope abundances Present and future missions such as Genesis, Stardust, Interstellar Pathfinder, and Interstellar Probe, improvements of remote sensing instrumentation and experiments on extraterrestrial material such as meteorites, presolar grains, and lunar or returned planetary or cometary samples will result in an improved database of elemental and isotopic abundances This includes the primordial abundances of D, ^3He, ^4He, and ^7Li, abundances of the heavier elements in stars and galaxies, the composition of the interstellar medium, solar wind and comets as well as the (highly) volatile elements in the solar system such as helium, nitrogen, oxygen or xenon
TL;DR: In this paper, the (p,gamma) cross section of Sr-84,Sr-86 and Sr-87 isotopes has been measured using activation technique in the proton energy range between 1.5 and 3 MeV.
01 May 2001
TL;DR: In this paper, the behavior of C/O and N/O ratios as a function of metallicity in HII regions in galaxies is characterised, and used to derive rough values of chemical yields from analytic models.
Abstract: The behaviour of C/O and N/O ratios as a function of metallicity in HII regions in galaxies is characterised, and used to derive rough values of chemical yields from analytic models. These ‘analytic yields’ are used to select the best available numerical yields from published stellar nucleosynthesis calculations. This gives a reasonably coherent picture of the important production sites of carbon and nitrogen, with carbon coming from massive stars and nitrogen from intermediate mass stars. The effects of gas inflow and stellar nucleosynthesis time-delay on element ratios C/O and N/O are expected to be small, but may be detectable for N/O. The small dispersion in values of N/O observed in low-metallicity blue compact dwarf galaxies may indicate that these systems have fairly long-lived quiescent star formation. Brief consideration of the CNO cycles suggests that the most recent values for the 17O(p,α)14N cross-section are certainly better than older values.
TL;DR: In this article, the behavior of C/O and N/O ratios as a function of metallicity in HII regions in galaxies is characterised, and used to derive rough values of chemical yields from analytic models.
Abstract: The behaviour of C/O and N/O ratios as a function of metallicity in HII regions in galaxies is characterised, and used to derive rough values of chemical yields from analytic models. These `analytic yields' are used to select the best available numerical yields from published stellar nucleosynthesis calculations. This gives a reasonably coherent picture of the important production sites of carbon and nitrogen, with carbon coming from massive stars and nitrogen from intermediate mass stars. The effects of gas inflow and stellar nucleosynthesis time-delay on element ratios C/O and N/O are expected to be small, but may be detectable for N/O. The small dispersion in values of N/O observed in low-metallicity blue compact dwarf galaxies may indicate that these systems have fairly long-lived quiescent star formation. Brief consideration of the CNO cycles suggests that the most recent values for the 17O(p,α)14N cross-section are certainly better than older values.
TL;DR: In this paper, the production of nuclei up to and including the weak s-process component at A ≈ 60-90 is calculated for all stages of stable and explosive nuclear burning in stars of 15, 20, and 25 M with initial solar metallicity.
01 Jan 2001
TL;DR: In this paper, a detailed standard chemical evolution model was developed to study the evolution of all the chemical elements up to the iron peak in the solar vicinity, and the model nicely reproduces the main observational constraints of the solar neighborhood.
Abstract: We have developed a detailed standard chemical evolution model to study the evolution of all the chemical elements up to the iron peak in the solar vicinity. We consider that the Galaxy was formed through two episodes of exponentially decreasing infall, out of extragalactic gas. In a rst infall episode, with a duration of 1 Gyr, the halo and the thick disk were assembled out of primordial gas, while the thin disk formed in a second episode of infall of slightly enriched extragalactic gas, with much longer timescale. The model nicely reproduces the main observational constraints of the solar neighborhood, and the calculated elemental abundances at the time of the solar birth are in excellent agreement with the solar abundances. By the inclusion of metallicity{dependent yields for the whole range of stellar masses we follow the evolution of 76 isotopes of all the chemical elements between hydrogen and zinc. Those results are compared with a large and recent body of observational data, and we discuss in detail the implications for stellar nucleosynthesis.
01 Jan 2001
TL;DR: In this paper, a full dynamical reaction network for both the a-rich freezeout and subsequent r-process is employed, and the physical properties of the neutrino-heated ejecta are deduced from a general relativistic model in which spherical symmetry and steadyow are assumed.
Abstract: We present calculations of r-process nucleosynthesis in neutrino-driven winds from the nascent neutron stars of core-collapse supernovae. A full dynamical reaction network for both the a-rich freezeout and the subsequent r-process is employed. The physical properties of the neutrino-heated ejecta are deduced from a general relativistic model in which spherical symmetry and steady —ow are assumed. Our results suggest that protoneutron stars with a large compaction ratio provide the most robust physical conditions for the r-process. The third peak of the r-process is well reproduced in the winds from these ii compact ˇˇ protoneutron stars even for a moderate entropy, and a D 100N A k¨200N A k, neutrino luminosity as high as D1052 ergs s~1. This is due to the short dynamical timescale of material in the wind. As a result, the overproduction of nuclei with is diminished (although some over- A ( 120 production of nuclei with A B 90 is still evident). The abundances of the r-process elements per event is signi—cantly higher than in previous studies. The total integrated nucleosynthesis yields are in good agreement with the solar r-process abundance pattern. Our results have con—rmed that the neutrino- driven wind scenario is still a promising site in which to form the solar r-process abundances. However, our best results seem to imply both a rather soft neutron-star equation of state and a massive proto¨ neutron star that is difficult to achieve with standard core-collapse models. We propose that the most favorable conditions perhaps require that a massive supernova progenitor forms a massive proto¨ neutron star by accretion after a failed initial neutrino burst. Subject headings: nuclear reactions, nucleosynthesis, abundancesstars: abundances ¨ stars: mass lossstars: neutronsupernovae: general
TL;DR: In this paper, the differences between field and globular cluster populations and their possible origin were discussed both in terms of primordial pollution and stellar internal nucleosynthesis and mixing, and the influence of metallicity and of a dense environment on abundance anomalies in connection with the second parameter problem and with the stellar yields.
Abstract: During the last two decades, extensive spectroscopic studies have revealed chemical abundance anomalies exhibited by low mass RGB stars which bring a new light on some important aspects of stellar nucleosynthesis and chemical evolution. We underline the differences between field and globular cluster populations and discuss their possible origin both in terms of primordial pollution and stellar internal nucleosynthesis and mixing. We suggest some tests to help to understand the influence of metallicity and of a dense environment on abundance anomalies in connection with the second parameter problem and with the stellar yields.