Chemical Self-Enrichment of HII Regions by the Wolf-Rayet Phase of an 85 Msun star

It is clear from stellar evolution and from observations of WR stars that massive stars are releasing metal-enriched gas through their stellar winds in the Wolf-Rayet phase. Although HII region spectra serve as diagnostics to determine the present-day chemical composition of the interstellar medium, it is far from being understood to what extent the HII gas is already contaminated by chemically processed stellar wind. Therefore, we analyzed our models of radiative and wind bubbles of an isolated 85 Msun star with solar metallicity (Kr\"oger et al. 2006) with respect to the chemical enrichment of the circumstellar HII region. Plausibly, the hot stellar wind bubble (SWB) is enriched with 14N during the WN phase and even much higher with 12C and 16O during the WC phase of the star. During the short period that the 85 Msun star spends in the WC stage enriched SWB material mixes with warm HII gas of solar abundances and thus enhances the metallicity in the HII region. However, at the end of the stellar lifetime the mass ratios of the traced elements N and O in the warm ionized gas are insignificantly higher than solar, whereas an enrichment of 22 % above solar is found for C. Important issues from the presented study comprise a steeper radial gradient of C than O and a decreasing effect of self-enrichment for metal-poor galaxies.Comment: 5 pages, 3 figures, accepted for publication in A&A Letter

Production of 92Nb, 92Mo, and 146Sm in the gamma-process in SNIa

The knowledge of the production of extinct radioactivities like 92Nb and 146Sm by photodisintegration processes in ccSN and SNIa models is essential for interpreting abundances in meteoritic material and for Galactic Chemical Evolution (GCE). The 92Mo/92Nb and 146Sm/144Sm ratios provide constraints for GCE and production sites. We present results for SNIa with emphasis on nuclear uncertainties.Comment: 6 pages, 4 figures, Proceedings of the 13th Symposium on Nuclei in the Cosmos (NIC XIII), July 2014, Debrecen, Hungar

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

Abundance Uncertainties Obtained With the PizBuin Framework For Monte Carlo Reaction Rate Variations

Uncertainties in nucleosynthesis models originating from uncertainties in astrophysical reaction rates were estimated in a Monte Carlo variation procedure. Thousands of rates were simultaneously varied within individual, temperature-dependent errors to calculate their combined effect on final abundances. After a presentation of the method, results from application to three different nucleosynthesis processes are shown: the $\gamma$-process and the s-process in massive stars, and the main s-process in AGB stars (preliminary results). Thermal excitation of nuclei in the stellar plasma and the combined action of several reactions increase the final uncertainties above the level of the experimental errors. The total uncertainty, on the other hand, remains within a factor of two even in processes involving a large number of unmeasured rates, with some notable exceptions for nuclides whose production is spread over several stellar layers and for s-process branchings.Comment: 8 pages, 4 figures; Proceedings of OMEG 2017, Daejeon, Korea, June 27-30, 2017; to appear in AIP Conf. Pro

Theory considerations for nucleosynthesis beyond Fe with special emphasis on p-nuclei in massive stars

T. Rauscher, N. Nishimura, and R. Hirschi, ‘Theory considerations for nucleosynthesis beyond Fe with special emphasis on p-nuclei in massive stars’, in proceedings CETUP* 2015 – Workshop on Dark Matter, Neutrino Physics and Astrophysics PPC 2015 – IXth International Conference on Interconnections between Particle Physics and Cosmology. Deadwood, South Dakota, USA. 15-17 July 2015. Barbara Szczerbinska, Rouzbeh Allahverdi, Kaladi Babu, Baha Balantekin, Bhaskar Dutta, Teruki Kamon, Jason Kumar, Farinaldo Queiroz, Louis Strigari, and Rebecca Surman eds., AIP Conference Proceedings 1743, 040008 (2016); doi: http://dx.doi.org/10.1063/1.4953300ISBN 9780735414006. Published by AIP Publishing.Nucleosynthesis of heavy elements requires the use of different experimental and theoretical methods to determine astrophysical reaction rates than light element nucleosynthesis. Additionally, there are also larger uncertainties involved in the astrophysical models, both because the sites are not well known and because of differing numerical treatments in different models. As an example for the latter, the production of p-nuclei is compared in two different stellar models, demonstrating that a model widely used for postproduction calculations may have a zone grid too coarse to follow the synthesis of p-nuclei in detail

The s-process nucleosynthesis : Impact of the uncertainties in the nuclear physics determined by monte carlo variations

We investigated the impact of uncertainties in neutron-capture and weak reactions (on heavy elements) on the s-process nucleosynthesis in low-mass stars and massive stars using a Monte-Carlo based approach. We performed extensive nuclear reaction network calculations that include newly evaluated temperature-dependent upper and lower limits for the individual reaction rates. We found β-decay rate uncertainties affect only a few nuclei near s-process branchings, whereas most of the uncertainty in the final abundances is caused by uncertainties in the neutron capture rates. We suggest a list of uncertain rates as candidates for improved measurement by future experiments.Peer reviewe

Intermittent convection, mixed boundary conditions and the stability of the thermohaline circulation

Intermittent convection and its consequences on the stability of the thermohaline circulation are investigated with an oceanic global circulation model (OGCM) and simple box models. A two-box model shows that intermittency is a consequence of the non-linearity of the equation of state and of the ratio of heat and freshwater fluxes at surface versus the fluxes at depth. Moreover, it only occurs in areas, where the instability of the water column is caused by temperature or by salinity. Intermittency is not necessarily suppressed by long restoring times. Because intermittent convection causes temporal variations of the ocean-atmosphere fluxes, an OGCM cannot reach an exact equilibrium. After a switch to mixed boundary conditions, changes of the convective activity occur in areas where intermittency is observed. Intermittent convection becomes either continuous or is stopped depending on the method used for calculating the freshwater fluxes. Advective and diffusive fluxes between these regions and their surroundings change in order to balance the altered convective fluxes. A comparison between the OGCM and a six-box model illustrates that this may lead to an alteration of adjacent deep convection and of the related deep water formation

The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations

We discuss the theoretical bases that underpin the automation of the computations of tree-level and next-to-leading order cross sections, of their matching to parton shower simulations, and of the merging of matched samples that differ by light-parton multiplicities. We present a computer program, MadGraph5_aMC@NLO, capable of handling all these computations -- parton-level fixed order, shower-matched, merged -- in a unified framework whose defining features are flexibility, high level of parallelisation, and human intervention limited to input physics quantities. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the LHC and to a 1-TeV $e^+e^-$ collider. While next-to-leading order results are restricted to QCD corrections to SM processes in the first public version, we show that from the user viewpoint no changes have to be expected in the case of corrections due to any given renormalisable Lagrangian, and that the implementation of these are well under way.Comment: 158 pages, 27 figures; a few references have been adde

Sensitivity to neutron captures and β-decays of the enhanced s-process in rotating massive stars at low metallicities

© 2018 IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. https://creativecommons.org/licenses/by/3.0/The s-process in massive stars, producing nuclei up to A ≈ 90, has a different behaviour at low metallicity if stellar rotation is significant. This enhanced s-process is distinct from the s-process in massive stars around solar metallicity, and details of the nucleosynthesis are poorly known. We investigated nuclear physics uncertainties in the enhanced s-process in metalpoor stars within a Monte-Carlo framework. We applied temperature-dependent uncertainties of reaction rates, distinguishing contributions from the ground state and from excited states. We found that the final abundance of several isotopes shows uncertainties larger than a factor of 2, mostly due to the neutron capture uncertainties. A few nuclei around branching points are affected by uncertainties in the β-decay.Peer reviewe