Mostrando recursos 61 - 80 de 194

  1. Gamma-ray spectrum of type Ia supernovae

    Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Gómez, J.; García Senz, Domingo; Jean, Pierre
    The explosion mechanism associated with thermonuclear supernovae (SNia) is still a matter of debate. In this paper we examine the 'f-ray emission of the radioactive debris predicted by the different theoretícal models and, using response estimations of the SPI and IBIS instruments aboard of INTEGRAL, we evaluate the capabilities of such instruments in the study of SNia. We also discuss preliminary results obtained with 3D models.

  2. Exploding stars: the gamma-ray signature of type Ia supernovae

    Isern Vilaboy, Jordi; Gomez, J.; Bravo Guil, Eduardo
    Type Ia supenovae are commonly thought to be the outcome of the thermonuclear explosion of a white dwarf in a binary system. Nevertheless, there is no agreement on the scenarios (double degenerates, symbiotics stars ...) able to produce such events nor on the mechanisms responsible of such explosions (central ignition of a carbon-oxygen mixture, off-center detonation of He...). In this paper we review the present status of the problem and we show, in the context of a CO central ignition, how γ-ray astronomy can provide useful constraints to the theoretical models.

  3. A new kind of type I supernovae?

    Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Domínguez, Inmaculada
    In this paper we examine the consequences of the propagation of a slow deflagration front through a C-0 white dwarf that leads to the formation of a marginally bound remnant. This situation corresponds to the transition between the Delayed Detonation models and the Pulsating Delayed Detonation ones. The radioactive decay of the freshly formed 56Ni not only powers the light curve but also produces an ablative front that finally disrupts the star. The light curve is characterized by its low luminosity {-16.8 m)-as compared with a normal SNia- and its broad peak (~ 100 days).

  4. SIXE (Spanish Italian X-ray Experiment): a summary of the phase-A study

    Giovannelli, F; Bravo Guil, Eduardo; García-Berro Montilla, Enrique
    In this paper we present a summary of the SIXE (Spanish Italian X-ray Experiment) for which we successfully finished the Phase-A study under financial support of the Spanish PNIE (Plan Nacional de Investigación Espacial).

  5. SIXE (Spanish Italian X-ray Experiment): a Payload for the Spanish MINISAT-02 Satellites

    Bravo Guil, Eduardo; García-Berro Montilla, Enrique; José Pont, Jordi; Giovannelli, F
    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 ΔE/E=60/E1/2 for E<35 KeV, the continuum sensitivity (3ơ in 105 s) of ~3•10-6ph/cm2 •KeV, the line detection sensitivity (3ơ 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 of...

  6. High-temperature combustion: Approaching equilibrium using nuclear networks

    Cabezón Gómez, Rubén Martín; García Senz, Domingo; Bravo Guil, Eduardo

  7. 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 Gabriel; 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.

  8. 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...

  9. 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...

  10. 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

  11. 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.; 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...

  12. Bounds on the possible evolution of the gravitational constant from cosmological type-Ia supernovae

    Gaztañaga, E.; García-Berro Montilla, Enrique; Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Domínguez, Inmaculada
    Recent high-redshift type-Ia supernovae results can be used to set new bounds on a possible variation of the gravitational constant G. If the local value of G at the space-time location of distant supernovae is different, it would change both the kinetic energy release and the amount of 56Ni synthesized in the supernova outburst. Both effects are related to a change in the Chandrasekhar mass MCh∝G-3/2. In addition, the integrated variation of G with time would also affect the cosmic evolution and therefore the luminosity distance relation. We show that the later effect in the magnitudes of type-Ia supernovae is...

  13. 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.

  14. 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...

  15. 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...

  16. 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.

  17. 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,...

  18. Collision of detonation waves and its implications in the nucleosynthesis of Type Ia supernovae

    García Senz, Domingo; Bravo Guil, Eduardo

  19. Exploring the physics of type Ia supernovae through the x-ray spectra of their remnants

    Badenes Montoliu, Carles; 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...

  20. 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.

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