Mostrando recursos 81 - 100 de 194

  1. Pulsating reverse detonation models of Type Ia supernovae. I. Detonation ignition

    Bravo Guil, Eduardo; García Senz, Domingo

  2. Beyond the bubble catastrophe of type Ia supernovae: Pulsating reverse detonation models

    Bravo Guil, Eduardo; García Senz, Domingo

  3. 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...

  4. Pulsating reverse detonation models of Type Ia supernovae. II. Explosion

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

  5. On the internal composition of white dwarfs

    Isern Vilaboy, Jordi; Bravo Guil, Eduardo; García-Berro Montilla, Enrique; Domínguez, Inmaculada; Salaris, M.
    Peer Reviewed

  6. Nucleosynthesis as a result of multiple delayed detonations in Type Ia Supernovae

    García Senz, Domingo; Bravo Guil, Eduardo
    The explosion of a white dwarf of mass 1.36 M⊙ has been simulated in three dimensions with the aid of a SPH code. The explosion follows the delayed detonation paradigm. In this case the deflagration-detonation transition is induced by the large corrugation of the flame front resulting from Rayleigh-Taylor instability and turbulence. The nucleosynthetic yields have been calculated, showing that some neutronized isotopes such as 54Fe or 58Ni are not overproduced with respect to the solar system ratios. The distribution of intermediate-mass elements is also compatible with the spectra of normal SNIa. The exception is, however, the abundance of carbon...

  7. The innermost ejecta of core collapse supernovae

    Fröhlich, C; Hauser, P; Liebendörfer, M; Martínez, G; Bravo Guil, Eduardo; Hix, W R; Zinner, N T; Thielemann, F -K
    We ensure successful explosions (of otherwise non-explosive models) by enhancing the neutrino luminosity via reducing the neutrino scattering cross sections or by increasing the heating efficiency via enhancing the neutrino absorption cross sections in the heating region. Our investigations show that the resulting electron fraction Ye in the innermost ejecta is close to 0.5, in some areas even exceeding 0.5. We present the effects of the resulting values for Ye on the nucleosynthesis yields of the innermost zones of core collapse Supernovae.

  8. Nucleosynthesis in neutrino-driven supernovae

    Froehlich, C; Hix, W R; Martínez, G; Liebendoerfer, M; Thielemann, F K; Bravo Guil, Eduardo; Langanke, K; Zinner, N T
    Core collapse supernovae are the leading actor in the story of the cosmic origin of the chemical elements. Existing models, which generally assume spherical symmetry and parameterize the explosion, have been able to broadly replicate the observed elemental pattern. However, inclusion of neutrino interactions produces noticeable improvements in the iron peak composition of the ejecta when compared to observations. Neutrino interactions may also provide a supernova source for light p-process nuclei.

  9. Gamma-ray emission from type Ia supernovae

    Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Hirschmann, Alina; García Senz, Domingo
    The explosion mechanism associated with thermonuclear supernovae is still a matter of debate. Since huge amounts of radioactive elements are synthesized during such explosions, it is possible to use the associated γ-ray emission as a diagnostic tool. In this paper we show, however, that for some values of the parameters that characterize the burning front propagation, the signatures overlap, thus avoiding a clear distinction among them. We also display some preliminary results obtained from 3-D simulations showing the influence of inhomogeneities in the γ-ray spectrum.

  10. Detection and interpretation of gamma-ray emission from SNIa

    Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Hirschmann, Alina
    The explosion mechanism associated with thermonuclear supernovae (SNIa) is still a matter of debate. Nevertheless, there is a wide agreement that large amounts of radioactive nuclei are produced during these events, which are expected to be strong γ-ray emitters. In this paper we investigate the usability of these γ-rays as a diagnostic tool. For this purpose we studied the variety of γ-ray spectra associated with the different currently-proposed SNIa explosion scenarios: detonation, deflagration, delayed detonation, and pulsating delayed detonation. Our study demonstrates that γ-ray emission from SNIa is indeed a promising tool, although care must be taken to avoid misinterpretations....

  11. Rotating type Ia SN progenitors: explosion and light curves

    Domínguez, Inmaculada; Piersanti, L.; Bravo Guil, Eduardo; Tornambé, A.; Straniero, O.; Gagliardi, S.
    Based on the rigidly rotating progenitor models found to be able to grow up to the canonical Chandrasekhar mass limit and beyond, and undergo a thermonuclear explosion, we compute the explosions, detailed nucleosynthesis, and corresponding light curves by means of a one-dimensional hydrodynamic code. Our results show that the inclusion of rotation in the evolution of the progenitors determines, in a natural way, a variation in the explosive physical conditions, mainly different explosive ignition densities (2.08 × 109 to 3.34 × 109 g cm-3), total masses (1.39-1.48 M), and binding energies (-5.3 × 1050 to -6.6 × 1050 ergs). Such...

  12. The evolution and C, N and O yields of intermediate-mass Z = 10-5 stars in isolation and in close binary systems

    Gil Pons, Pilar; Doherty, Carolyn L.; Suda, T.; Campbell, Simon; Lau, H.; Mansouri Guilani, Shervin; Lattanzio, John
    We have computed the evolution of Z = 10−5 stars of masses between 4 and 9 M , from their main sequence till the late TP-(S)AGB phase.We use a recent version of the Mount Stromlo Stellar Evolution code, in which molecular opacities include the effects of variable C/O abundances ratio, [1]. By computing hundreds (or thousands) of thermal pulses, we have been able either to remove the bulk of the stellar envelopes or to obtain stellar cores very close to MCh. Using [2] prescription for the mass loss rates the computed stars lose their envelopes before their cores reach MCh. This would forbid the occurrence of...

  13. Single and multiple detonations in white dwarfs

    García Senz, Domingo; Bravo Guil, Eduardo; Woosley, S
    A currently favored model for Type Ia supernovae consists of a carbon-oxygen (CO) white dwarf ( 0.6–1.0 M), surrounded by a thick layer of helium ( 0.2–0.3 M), which explodes as a consequence of successive detonations in the helium layer and the CO core. Previous studies, carried out in one and two dimensions, have shown that this model is capable of providing light curves and late-time spectra in agreement with observations, though the peak light spectrum may be problematic. These same studies also highlighted a key uncertainty in the model. When properly considered in three dimensions, will the helium detonation...

  14. A three-dimensional picture of the delayed-detonation model of type Ia supernovae

    Bravo Guil, Eduardo; García Senz, Domingo
    Aims. Deflagration models poorly explain the observed diversity of SNIa. Current multidimensional simulations of SNIa predict a significant amount of, so far unobserved, carbon and oxygen moving at low velocities. It has been proposed that these drawbacks can be resolved if there is a sudden jump to a detonation (delayed detonation), but these kinds of models have been explored mainly in one dimension. Here we present new three-dimensional delayed detonation models in which the deflagraton-to-detonation transition (DDT) takes place in conditions like those favored by one-dimensional models. Methods. We have used a smoothed-particle-hydrodynamics code adapted to follow all the dynamical phases...

  15. The contribution of Type IA supernovae to the galactic iron abundances

    Bravo Guil, Eduardo; Isern Vilaboy, Jordi; Canal Corretger, Ramon
    The thermonuclear explosion of a mass-accreting white dwarf in a close binary system is thought to be at the origin of Type Ia supernovae. Standard models, which ignite carbon at densities higher than 2-4 x 10 exp 9 g/cu cm, give, however, a large production of species like Fe-54, Ni-58, and Cr-54, which has been regarded as incompatible with the solar system abundances. In this paper we analyze the weight of the constraints imposed by nucleosynthesis of the Fe-peak nuclides to the aforementioned scenario for Type Ia supernovae when the contribution of Type II and Type Ib supernovae to the...

  16. On the photometric homogeneity of type IA supernovae

    Bravo Guil, Eduardo; Domínguez, Inmaculada; Isern Vilaboy, Jordi; Canal Corretger, Ramon; Höflich, P.; Labay, Javier
    The dependence of the characteristics of the light curves of Type Ia supernovae on the ignition density of the progenitor white dwarf is studied with the aid of two models of propagation of the thermonuclear burning front: as a deflagration and as a delayed detonation. The light curve is computed from opacities which take into account the velocity gradients. The results show that in all cases the resulting light curves roughly agree with observations and that they are not sensitive to the ignition density of the white dwarf. Only the model corresponding to a deflagration starting at a density of...

  17. Clues to type ia supernovae progenitors from degenerate carbon ignition models

    Bravo Guil, Eduardo; Tornambé, A; Domínguez, Inmaculada; Isern Vilaboy, Jordi
    Peer Reviewed

  18. Axisymmetric smoothed particle hydrodynamics with self-gravity

    García Senz, Domingo; Relano, A; Cabezón Gómez, Rubén Martín; Bravo Guil, Eduardo
    The axisymmetric form of the hydrodynamic equations within the smoothed particle hydrodynamics (SPH) formalism is presented and checked using idealized scenarios taken from astrophysics (free fall collapse, implosion and further pulsation of a Sun-like star), gas dynamics (wall heating problem, collision of two streams of gas) and inertial confinement fusion (ablative implosion of a small capsule). New material concerning the standard SPH formalism is given. That includes the numerical handling of those mass points which move close to the singularity axis, more accurate expressions for the artificial viscosity and the heat conduction term and an easy way to incorporate self-gravity...

  19. Detailed spectral modeling of a three-dimensional pulsating reverse detonation model: Too much nickel

    Baron, E; Jeffery, D J; Branch, D; Bravo Guil, Eduardo; García Senz, Domingo; Hauschildt, P H
    We calculate detailed non-LTE synthetic spectra of a pulsating reverse detonation (PRD) model, a novel explosion mechanism for Type Ia supernovae. While the hydro models are calculated in three dimensions, the spectra use an angle-averaged hydro model and thus some of the three-dimensional (3D) details are lost, but the overall average should be a good representation of the average observed spectra. We study the model at three epochs: maximum light, 7 days prior to maximum light, and 5 days after maximum light. At maximum the defining Si II feature is prominent, but there is also a prominent C II feature,...

  20. The end of amnesia: A new method for measuring the metallicity of Type Ia supernova progenitors using manganese lines in supernova remnants

    Badenes Montoliu, Carles; Bravo Guil, Eduardo; Hughes, J.P.
    We propose a new method to measure the metallicity of Type Ia supernova progenitors using Mn and Cr lines in the X-ray spectra of young supernova remnants. We show that the Mn-to-Cr mass ratio in Type Ia supernova ejecta is tightly correlated with the initial metallicity of the progenitor, as determined by the neutron excess of the white dwarf material before thermonuclear runaway. We use this correlation, together with the flux of the Cr and Mn Kα X-ray lines in the Tycho supernova remnant recently detected by Suzaku, to derive a metallicity of log (Z) = − 1.32+ 0.67−0.33 for...

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