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Nomenclatura Unesco > (21) Astronomía y Astrofísica

Mostrando recursos 141 - 160 de 548

141. White dwarf mergers and the origin of R coronae borealis stars - Lorén Aguilar, Pablo; Longland, Richard Leigh; José Pont, Jordi; García-Berro Montilla, Enrique; Althaus, Leandro G.; Isern-Fontanet, J.
We present a nucleosynthesis study of the merger of a 0.4 M⊙ helium white dwarf with a 0.8 M⊙ carbon-oxygen white dwarf, coupling the thermodynamic history of Smoothed Particle Hydrodynamics particles with a post-processing code.The resulting chemical abundance pattern, particularly for oxygen and fluorine, is inqualitative agreement with the observed abundances in R Coronae Borealis stars.

142. Interaction of Supernovae remnants: From the circumstellar medium to the terrestrial laboratory - Velarde, P; García Senz, Domingo; Bravo Guil, Eduardo; Ogando, F; Relaño, A; Oliva, E
The evolution of supernova remnants (SNRs) represents a useful and natural laboratory for gasdynamics studies. In this paper the results of several hydrodynamical simulations of the propagation and early phases of interaction of two SNRs embedded in a homogeneous interstellar environment are shown. In particular, the hydrodynamic evolution and collision of twin SNRs during their self-similar stage has been simulated using a two-dimensional Lagrangian hydrocode. In addition, the results of a detailed simulation that attempts to set the adequate conditions to reproduce the same phenomenon through laser ablation of two plastic plugs at the laboratory scale are presented. These results...

143. Consequences of the Collision Between the Gas Ejected in the Collapse of a White Dwarf and a Low-Mass Star - Serichol Augué, Núria; García Senz, Domingo; Bravo Guil, Eduardo

144. Unified one-dimensional simulations of gamma-ray line emission from type Ia supernovae - Milne, P A; Hungerford, A L; Fryer, C L; Evans, T M; Urbatsch, T J; Boggs, S E; Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Hirschmann, A; Kumagai, S; Pinto, P A; The, L S
The light curves of Type Ia supernovae (SNe Ia) are powered by gamma rays emitted by the decay of radioactive elements such as 56Ni and its decay products. These gamma rays are downscattered, absorbed, and eventually reprocessed into the optical emission that makes up the bulk of all SN observations. Detection of the gamma rays that escape the expanding star provide the only direct means to study this power source for SN Ia light curves. Unfortunately, disagreements between calculations for the gamma-ray lines have made it difficult to interpret any gamma-ray observations. Here we present a detailed comparison of the...

145. SIXE: A Payload for MINISAT-02 - Gómez, J; Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Giovannelli, F; Padula, C L
A description of the X-ray instrument SIXE proposed for the MINISAT-02 mission is presented. The description includes the scientific goals and instrument performances.

146. A particle code for deflagrations in white dwarfs. I. Numerical techniques - García Senz, Domingo; Bravo Guil, Eduardo; Serichol Augué, Núria
In this paper we report some specific features of the numerical technique used to study the dynamic evolution of massive white dwarfs following the explosive ignition of nuclear fuel under degenerate conditions. We focus on three important points: (1) how to construct a stable initial model for white dwarfs with a central density ρc > 109 g cm-3 in the context of smoothed particle hydrodynamics (SPH); (2) the procedure devised in the numerical handling of combustion fronts and thermal discontinuities; and (3) a proposed method based on techniques of analysis of dynamic sets of points to characterize the flame front...

147. Constraining deflagration models of type Ia supernovae through intermediate-mass elements - García Senz, Domingo; Bravo Guil, Eduardo; Cabezón Gómez, Rubén Martín; Woosley, S E
The physical structure of a nuclear flame is a basic ingredient of the theory of Type Ia supernovae (SNe Ia). Assuming an exponential density reduction with several characteristic times, we have followed the evolution of a planar nuclear flame in an expanding background from an initial density of 6.6 × 107 g cm-3 down to 2 × 106 g cm-3. The total amount of synthesized intermediate-mass elements (IMEs), from silicon to calcium, was monitored during the calculation. We have used the computed mass fractions, XIME, of these elements to estimate the total amount of IMEs synthesized during the deflagration of...

148. Neutrino-induced nucleosynthesis of a > 64 nuclei: The vp process - Fröhlich, C; Martínez, G; Liebendörfer, M; Thielemann, F -K; Bravo Guil, Eduardo; Hix, W R; Langanke, K; Zinner, N T
We present a new nucleosynthesis process that we denote as the νp process, which occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino fluxes create proton-rich ejecta. In this process, antineutrino absorptions in the proton-rich environment produce neutrons that are immediately captured by neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with mass numbers A>64, making this process a possible candidate to explain the origin of the solar abundances of 92,94Mo and 96,98Ru. This process also offers a natural explanation for the large abundance of Sr seen in a hyper-metal-poor star.

149. Composition of the innermost core-collapse supernova ejecta - Fröhlich, C; Hauser, P; Liebendörfer, M; Martínez, G; Thielemann, F -K; Bravo Guil, Eduardo; Zinner, N T; Hix, W R; Langanke, K; Mezzacappa, A; Nomoto, K
With currently known input physics and computer simulations in one dimension, a self-consistent treatment of core-collapse supernovae does not yet lead to successful explosions, while two-dimensional models show some promise. Thus, there are strong indications that the delayed neutrino mechanism works combined with a multidimensional convection treatment for unstable layers (possibly with the aid of rotation, magnetic fields and/or still existent uncertainties in neutrino opacities). On the other hand, there is a need to provide correct nucleosynthesis abundances for the progressing field of galactic evolution and observations of low-metallicity stars. The innermost ejecta is directly affected by the explosion mechanism,...

150. Collision of detonation waves and its implications in the nucleosynthesis of Type Ia supernovae - García Senz, Domingo; Bravo Guil, Eduardo

151. Exploring the physics of type Ia supernovae through the x-ray spectra of their remnants - Badenes, C; Borkowski, K; Bravo Guil, Eduardo; Hughes, J P; Hwang, U
We present the results of an ongoing project to use the X-ray observations of Type Ia Supernova Remnants to constrain the physical processes involved in Type Ia Supernova explosions. We use the Tycho Supernova Remnant (SN 1572) as a benchmark case, comparing its observed spectrum with models for the X-ray emission from the shocked ejecta generated from di erent kinds of Type Ia explosions. Both the integrated spectrum of Tycho and the spatial distribution of the Fe and Si emission in the remnant are well reproduced by delayed detonation models with stratified ejecta. All the other Type Ia explosion models...

152. Smooth particle hydrodynamics simulations of deflagrations in supernovae - Bravo Guil, Eduardo; García Senz, Domingo
Some results of a set of tridimensional calculations concerning the explosion of a white dwarf by means of a smooth particle hydrodynamics (SPH) code are presented. The burning front advance is solved along with the hydrodynamics of the whole star, and a characterization of the front surface in terms of fractal concepts is done. Our main result indicates that the surface of the deflagration front sought at the largest scales of the Rayleigh-Taylor instability can be characterized as a fractal with a time-dependent dimension, D(t), whose value is 2 ≤ D(t) ≤ 2.4.

153. Pulsating reverse detonation models of Type Ia supernovae. I. Detonation ignition - Bravo Guil, Eduardo; García Senz, Domingo

154. Beyond the bubble catastrophe of type Ia supernovae: Pulsating reverse detonation models - Bravo Guil, Eduardo; García Senz, Domingo

155. SIXE: An X-ray experiment for the MINISAT platform - Bravo Guil, Eduardo; García-Berro Montilla, Enrique; Gutierrez Cabello, Jorge Luis; José Pont, Jordi; García Senz, Domingo; Cabestany Moncusí, Joan; Madrenas Boadas, Jordi
SIXE (Spanish Italian X-ray Experiment) is an X-ray payload with geometric area of ~3200 cm2 , formed by four identical gas-filled Multiwire Proportional Counters devoted for a long term spectroscopy of selected X-ray sources in the energy range ~3-60 KeV. The spectral resolution of ~5% for E>35 KeV and ¿E/E=60/E1/2 for E<35 KeV, the continuum sensitivity (3o in 105 s) of ~3•10-6ph/cm2 •KeV, the line detection sensitivity (3o in 105 s) of ~3.5•10-6ph /cm2 •KeV, the time accuracy of 0.1 ms, the experiment weight of ~90 Kg, the full dimensions including the electronic box of ~660x660x400 mm3, the power budget...

156. Pulsating reverse detonation models of Type Ia supernovae. II. Explosion - Bravo Guil, Eduardo; García Senz, Domingo; Cabezón Gómez, Rubén Martín; Domínguez, I
Observational evidences point to a common explosion mechanism of Type Ia supernovae based on a delayed detonation of a white dwarf (WD). However, all attempts to find a convincing ignition mechanism based on a delayed detonation in a destabilized, expanding, white dwarf have been elusive so far. One of the possibilities that has been invoked is that an inefficient deflagration leads to pulsation of a Chandrasekhar-mass WD, followed by formation of an accretion shock that confines a carbon–oxygen rich core, while transforming the kinetic energy of the collapsing halo into thermal energy of the core, until an inward moving detonation...

157. High-temperature combustion: Approaching equilibrium using nuclear networks - Cabezón Gómez, Rubén Martín; García Senz, Domingo; Bravo Guil, Eduardo

158. White dwarf mergers and the origin of R coronae borealis stars - Lorén Aguilar, Pablo; Longland, Richard Leigh; José Pont, Jordi; García-Berro Montilla, Enrique; Althaus, Leandro G.; Isern-Fontanet, J.
We present a nucleosynthesis study of the merger of a 0.4 M⊙ helium white dwarf with a 0.8 M⊙ carbon-oxygen white dwarf, coupling the thermodynamic history of Smoothed Particle Hydrodynamics particles with a post-processing code. The resulting chemical abundance pattern, particularly for oxygen and fluorine, is in qualitative agreement with the observed abundances in R Coronae Borealis stars.

159. Interaction of Supernovae remnants: From the circumstellar medium to the terrestrial laboratory - Velarde, P; García Senz, Domingo; Bravo Guil, Eduardo; Ogando, F; Relaño, A; Oliva, E
The evolution of supernova remnants (SNRs) represents a useful and natural laboratory for gasdynamics studies. In this paper the results of several hydrodynamical simulations of the propagation and early phases of interaction of two SNRs embedded in a homogeneous interstellar environment are shown. In particular, the hydrodynamic evolution and collision of twin SNRs during their self-similar stage has been simulated using a two-dimensional Lagrangian hydrocode. In addition, the results of a detailed simulation that attempts to set the adequate conditions to reproduce the same phenomenon through laser ablation of two plastic plugs at the laboratory scale are presented. These results...

160. Production of intermediate-mass and heavy nuclei - Thielemann, F. K.; Frölich, Carla; Hirschi, R.; Liebendörfer, M.; Dillmann, I.; Mocelj, D.; Rauscher, t.; Martínez Pinedo, Gabriel; Langanke, K; Farouqi, K; Kratz, K.L.; Pfeiffer, B.; Panov, I.; Nadyozhin, D.K.; Blinnikov, S.; Bravo Guil, Eduardo; Hix, W.R.; Höflich, P.; Zinner, Ernst
Nucleosynthesis is the science related to all astrophysical processes which are responsible for the abundances of the elements and their isotopes in the universe. The astrophysical sites are the big bang and stellar objects. The working of nucleosynthesis processes is presented in a survey of events which act as abundance sources. For intermediate-mass and heavy elements, these are stellar evolution, type Ia and core collapse supernovae as well as hypernovae. We discuss successes and failures of existing processes and possible solutions via new (hitherto unknown) processes. Finally an analysis of their role is given in the puzzle to explain the...

 

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