Models for Type Ia supernovae and related astrophysical transients

We give an overview of recent efforts to model Type Ia supernovae and related astrophysical transients resulting from thermonuclear explosions in white dwarfs. In particular we point out the challenges resulting from the multi-physics multi-scale nature of the problem and discuss possible numerical approaches to meet them in hydrodynamical explosion simulations and radiative transfer modeling. We give examples of how these methods are applied to several explosion scenarios that have been proposed to explain distinct subsets or, in some cases, the majority of the observed events. In case we comment on some of the successes and shortcoming of these scenarios and highlight important outstanding issues.Comment: 20 pages, 2 figures, review published in Space Science Reviews as part of the topical collection on supernovae, replacement corrects typos in the conclusions sectio

A parameter-free optical potential for the heavy-ion elastic scattering process

Thirty elastic scattering angular distributions for seven heavy-ion systems, in wide energy ranges, have been studied with the aim of systematizing the optical potential, real and imaginary parts, in a global way. The framework is: i) an extensive systematization of nuclear densities, ii) the energy dependence of the bare potential accounted by a model based on the nonlocal nature of the interaction, and iii) the real and imaginary parts of the optical potential assumed to have the same radial shape.Comment: 5 pages, 8 figure

Processamento de imagens: conceitos básicos relacionados com o fenômeno de difração e uso de um computador óptico

O fenômeno de difração é utilizado em um experimento relacionado à óptica de Fourier com o objetivo de estudar conceitos básicos de processamento de imagens. Um computador óptico e programas de suporte são utilizados de maneira que os estudantes tenham contato com procedimentos de filtragem espacial e reconstrução da imagem processada

A supersonic jet target for the cross section measurement of the 12 C(α, γ) 16 O reaction with the recoil mass separator ERNA

12C(α, γ)16O cross section plays a key-role in the stellar evolution and nucleosynthesis of massive stars. Hence, it must be determined with the precision of about 10% at the relevant Gamow energy of 300 keV. The ERNA (European Recoil mass separator for Nuclear Astrophysics) collaboration measured, for the first time, the total cross section of 12C(α, γ)16O by means of the direct detection of the 16O ions produced in the reaction down to an energy of Ecm = 1.9 MeV. To extend the measurement at lower energy, it is necessary to limit the extension of the He gas target. This can be achieved using a supersonic jet, where the oblique shock waves and expansion fans formed at its boundaries confine the gas, which can be efficiently collected using a catcher. A test version of such a system has been designed, constructed and experimentally characterized as a bench mark for a full numerical simulation using FV (Finite Volume) methods. The results of the commissioning of the jet test version and the design of the new system that will be used in combination with ERNA are presented and discussed

Quantum physics of stars

International audienceStars are slowly developing objects; the lifetimes of the different burning phases are determined by the strength of nuclear reactions, which in turn are defined by the quantum structure of the associated nuclei at the threshold and the respective reaction mechanisms. Stars, from the nuclear physics perspective, are cold environments where only a few of the key nuclear reactions have been measured at the actual stellar plasma temperatures. This is also the case for more dynamic astrophysical phenomena from the big bang to stellar explosions. Most of the nuclear reaction rates are therefore based on theoretical extrapolations. A number of discrepancies between these predictions and the associated stellar signatures have been observed, and many may be due to low-energy or near-threshold quantum effects. These effects need to be understood in order to reliably model nuclear reaction processes, not only for stars but also for low-temperature plasma environments such as controlled magnetic or inertial confinement fusion systems, which operate in similar temperature regimes. This review summarizes the various theoretical techniques presently used for deriving reaction rates and discusses possible quantum effects that may impact the reaction cross section near the reaction threshold. These resemble enhanced single-particle and cluster structures near threshold and associated interference effects. New experimental techniques such as deep-underground accelerators or the study of transfer reactions to mimic the quantum-mechanical transition strength, the so-called Trojan horse method, provide ways to directly or indirectly probe the reaction features that determine the reaction rates at stellar energies. This is demonstrated on a number of key nuclear reactions for different nucleosynthesis environments. Finally, current inconsistencies between experimental predictions and observations are discussed