Boron depletion in 9 to 15 M(circle dot) stars with rotation

The treatment of mixing is still one of the major uncertainties in stellar evolution models. One open question is how well the prescriptions for rotational mixing describe the real effects. We tested the mixing prescriptions included in the Geneva stellar evolution code (GENEC) by following the evolution of surface abundances of light isotopes in massive stars, such as boron and nitrogen. We followed 9, 12 and 15 M(O) models with rotation from the zero age main sequence up to the end of He burning. The calculations show the expected behaviour with faster depletion of boton for faster rotating stars and more massive stars. The mixing at the surface is more efficient, than predicted by prescriptions used in other codes and reproduces the majority of observations very well However two observed stars with strong boron depletion but, no nitrogen enhancement still can not be explained and let the question open whether additional mixing processes are acting in these massive star

Boron depletion in 9 to 15 M stars with rotation

The treatment of mixing is still one of the major uncertainties in stellar evolution models. One open question is how well the prescriptions for rotational mixing describe the real effects. We tested the mixing prescriptions included in the Geneva stellar evolution code (GENEC) by following the evolution of surface abundances of light isotopes in massive stars, such as boron and nitrogen. We followed 9, 12 and 15 M models with rotation from the zero age main sequence up to the end of He burning. The calculations show the expected behaviour with faster depletion of boron for faster rotating stars and more massive stars. The mixing at the surface is more efficient than predicted by prescriptions used in other codes and reproduces the majority of observations very well. However two observed stars with strong boron depletion but no nitrogen enrichment still can not be explained and let the question open whether additional mixing processes are acting in these massive star

Statics and dynamics of weakly coupled antiferromagnetic spin-1/2 ladders in a magnetic field

We investigate weakly coupled spin-1/2 ladders in a magnetic field. The work is motivated by recent experiments on the compound (C5H12N)2CuBr4 (BPCB). We use a combination of numerical and analytical methods, in particular the density matrix renormalization group (DMRG) technique, to explore the phase diagram and the excitation spectra of such a system. We give detailed results on the temperature dependence of the magnetization and the specific heat, and the magnetic field dependence of the nuclear magnetic resonance (NMR) relaxation rate of single ladders. For coupled ladders, treating the weak interladder coupling within a mean-field or quantum Monte Carlo approach, we compute the transition temperature of triplet condensation and its corresponding antiferromagnetic order parameter. Existing experimental measurements are discussed and compared to our theoretical results. Furthermore we compute, using time dependent DMRG, the dynamical correlations of a single spin ladder. Our results allow to directly describe the inelastic neutron scattering cross section up to high energies. We focus on the evolution of the spectra with the magnetic field and compare their behavior for different couplings. The characteristic features of the spectra are interpreted using different analytical approaches such as the mapping onto a spin chain, a Luttinger liquid (LL) or onto a t-J model. For values of parameters for which such measurements exist, we compare our results to inelastic neutron scattering experiments on the compound BPCB and find excellent agreement. We make additional predictions for the high energy part of the spectrum that are potentially testable in future experiments.Comment: 35 pages, 26 figure

Application of a theory and simulation-based convective boundary mixing model for AGB star evolution and nucleosynthesis

The s-process nucleosynthesis in Asymptotic giant branch (AGB) stars depends on the modeling of convective boundaries. We present models and s-process simulations that adopt a treatment of convective boundaries based on the results of hydrodynamic simulations and on the theory of mixing due to gravity waves in the vicinity of convective boundaries. Hydrodynamics simulations suggest the presence of convective boundary mixing (CBM) at the bottom of the thermal pulse-driven convective zone. Similarly, convection-induced mixing processes are proposed for the mixing below the convective envelope during third dredge-up (TDU), where the ¹³C pocket for the s process in AGB stars forms. In this work, we apply a CBM model motivated by simulations and theory to models with initial mass M=2 and M = 3 Mʘ, and with initial metal content Z = 0.01 and Z = 0.02. As reported previously, the He-intershell abundances of ¹²C and ¹⁶O are increased by CBM at the bottom of the pulse-driven convection zone. This mixing is affecting the ²²Ne(α, n)²⁵Mg activation and the s-process efficiency in the ¹³C-pocket. In our model, CBM at the bottom of the convective envelope during the TDU represents gravity wave mixing. Furthermore, we take into account the fact that hydrodynamic simulations indicate a declining mixing efficiency that is already about a pressure scale height from the convective boundaries, compared to mixing-length theory. We obtain the formation of the ¹³C-pocket with a mass of ≈10⁻⁴ Mʘ. The final s-process abundances are characterized by 0.36 < [s Fe] < 0.78 and the heavy-to-light s-process ratio is -0.23 < [hs ls] < 0.45. Finally, we compare our results with stellar observations, presolar grain measurements and previous work

Galactic Abundances: Report of Working Group 3

We summarize the various methods and their limitations and strengths to derive galactic abundances from in-situ and remote-sensing measurements, both from ground-based observations and from instruments in space. Because galactic abundances evolve in time and space it is important to obtain information with a variety of different methods covering different regions from the Very Local Insterstellar Medium (VLISM) to the distant galaxy, and different times throughout the evolution of the galaxy. We discuss the study of the present-day VLISM with neutral gas, pickup ions, and Anomalous Cosmic Rays, the study of the local interstellar medium (ISM) at distances <1.5 kpc utilizing absorption line measurements in H I clouds, and the study of galactic cosmic rays, sampling contemporary (~15 Myr) sources in the local ISM within a few kiloparsec of the solar system. Solar system abundances, derived from solar abundances and meteorite studies are discussed in several other chapters of this volume. They provide samples of matter from the ISM from the time of solar system format ion, about 4.5 Gyr ago. The evolution of galactic abundances on longer time scales is discussed in the context of nuclear synthesis in the various contributing stellar objects

Type Ia Supernovae: Influence of the Initial Composition on the Nucleosynthesis, Light Curves, Spectra and Consequences for the Determination of Omega_M & Lambda

The influence of the initial composition of the exploding white dwarf on the nucleosynthesis, light curves and spectra of Type Ia supernovae has been studied in order to evaluate the size of evolutionary effects on cosmological time scales, how the effects can be recognized and how one may be able to correct for them. The calculations are based on a set of delayed detonation models which give a good account of the optical and infrared light curves and of the spectral evolution. The explosions and light curves are calculated using a one- dimensional Lagrangian radiation-hydro code including a nuclear network. NLTE- spectra are computed for various epochs using the structure resulting from the light curve code. The following questions are addressed : What do we learn about the progenitor evolution and its metallicity? What are the systematic effects for the determination of the cosmological parameters $\Omega_M$ and $\Lambda$ and how can we recognize this potential 'pitfalls' and correct for evolutionary effects?Comment: 19 pages, TeX, Ap

Population III stars and the Long Gamma Ray Burst rate

Because massive, low-metallicity population III (PopIII) stars may produce very powerful long gamma-ray bursts (LGRBs), high-redshift GRB observations could probe the properties of the first stars. We analyze the correlation between early PopIII stars and LGRBs by using cosmological N-body/hydrodynamical simulations, which include detailed chemical evolution, cooling, star formation, feedback effects and the transition between PopIII and more standard population I/II (PopII/I) stars. From the Swift observed rate of LGRBs, we estimate the fraction of black holes that will produce a GRB from PopII/I stars to be in the range 0.028<f_{GRB}<0.140, depending on the assumed upper metallicity of the progenitor. Assuming that as of today no GRB event has been associated to a PopIII star, we estimate the upper limit for the fraction of LGRBs produced by PopIII stars to be in the range 0.006<f_{GRB}<0.022. When we apply a detection threshold compatible with the BAT instrument, we find that the expected fraction of PopIII GRBs (GRB3) is ~10% of the full LGRB population at z>6, becoming as high has 40% at z>10. Finally, we study the properties of the galaxies hosting our sample of GRB3. We find that the average metallicity of the galaxies hosting a GRB3 is typically higher than the critical metallicity used to select the PopIII stars, due to the efficiency in polluting the gas above such low values. We also find that the highest probability of finding a GRB3 is within galaxies with a stellar mass <10^7 Msun, independently from the redshift.Comment: 8 pages,3 figures. Submitted to MNRAS, revised version after referee's comment

The Nuclear Reaction Network WinNet

© 2023. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We present the state-of-the-art single-zone nuclear reaction network WinNet, which is capable of calculating the nucleosynthetic yields of a large variety of astrophysical environments and conditions. This ranges from the calculation of the primordial nucleosynthesis, where only a few nuclei are considered, to the ejecta of neutron star mergers with several thousands of involved nuclei. Here we describe the underlying physics and implementation details of the reaction network. We additionally present the numerical implementation of two different integration methods, the implicit Euler method and Gears method, along with their advantages and disadvantages. We furthermore describe basic example cases of thermodynamic conditions that we provide together with the network and demonstrate the reliability of the code by using simple test cases. With this publication, WinNet will be publicly available and open source at GitHub and Zenodo.Peer reviewe

The s Process: Nuclear Physics, Stellar Models, Observations

Nucleosynthesis in the s process takes place in the He burning layers of low mass 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 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.Comment: 53 pages, 20 figures, 3 tables; Reviews of Modern Physics, accepte

Massive stars as thermonuclear reactors and their explosions following core collapse

Nuclear reactions transform atomic nuclei inside stars. This is the process of stellar nucleosynthesis. The basic concepts of determining nuclear reaction rates inside stars are reviewed. How stars manage to burn their fuel so slowly most of the time are also considered. Stellar thermonuclear reactions involving protons in hydrostatic burning are discussed first. Then I discuss triple alpha reactions in the helium burning stage. Carbon and oxygen survive in red giant stars because of the nuclear structure of oxygen and neon. Further nuclear burning of carbon, neon, oxygen and silicon in quiescent conditions are discussed next. In the subsequent core-collapse phase, neutronization due to electron capture from the top of the Fermi sea in a degenerate core takes place. The expected signal of neutrinos from a nearby supernova is calculated. The supernova often explodes inside a dense circumstellar medium, which is established due to the progenitor star losing its outermost envelope in a stellar wind or mass transfer in a binary system. The nature of the circumstellar medium and the ejecta of the supernova and their dynamics are revealed by observations in the optical, IR, radio, and X-ray bands, and I discuss some of these observations and their interpretations.Comment: To be published in " Principles and Perspectives in Cosmochemistry" Lecture Notes on Kodai School on Synthesis of Elements in Stars; ed. by Aruna Goswami & Eswar Reddy, Springer Verlag, 2009. Contains 21 figure