Enrique Garcia-Berro

Publications (77) View all

• Article: Explaining the type Ia supernova PTF 11kx with a violent-prompt merger scenario

  Noam Soker, Amit Kashi, Enrique Garcia-Berro, Santiago Torres, Judit Camacho
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  ABSTRACT: We argue that the multiple shells of circumstellar material (CSM) and the supernovae (SN) ejecta interaction with the CSM starting 59 days after the explosion of the Type Ia SN (SN Ia) PTF 11kx, are best described by a violent prompt merger. In this prompt merger scenario the common envelope (CE) phase is terminated by a merger of a WD companion with the hot core of a massive asymptotic giant (AGB) star. In most cases the WD is disrupted and accreted onto the more massive core. However, in the rare cases where the merger takes place when the WD is denser than the core, the core will be disrupted and accreted onto the cooler WD. In such cases the explosion might occur with no appreciable delay, i.e., months to years after the termination of the CE phase. This, we propose, might be the evolutionary route that could lead to the explosion of PTF 11kx. This scenario can account for the very massive CSM within ~1000 AU of the exploding PTF 11kx star, for the presence of hydrogen, and for the presence of shells in the CSM.
  07/2012;
• Source

  Available from: Enrique Garcia-Berro

  Article: Mixing in classical novae: a 2-D sensitivity study

  Jordi Casanova, Jordi Jose, Enrique Garcia-Berro, Alan Calder, Steven N. Shore
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  ABSTRACT: Classical novae are explosive phenomena that take place in stellar binary systems. They are powered by mass transfer from a low-mass, main sequence star onto a white dwarf. The material piles up under degenerate conditions and a thermonuclear runaway ensues. The energy released by the suite of nuclear processes operating at the envelope heats the material up to peak temperatures of ~ (1 - 4) \times 108 K. During these events, about 10-4 - 10-5 M\odot, enriched in CNO and other intermediate-mass elements, are ejected into the interstellar medium. To account for the gross observational properties of classical novae (in particular, a metallicity enhancement in the ejecta above solar values), numerical models assume mixing between the (solar-like) material transferred from the companion and the outermost layers (CO- or ONe-rich) of the underlying white dwarf. The nature of the mixing mechanism that operates at the core-envelope interface has puzzled stellar modelers for about 40 years. Here we investigate the role of Kelvin-Helmholtz instabilities as a natural mechanism for self-enrichment of the accreted envelope with core material. The feasibility of this mechanism is studied by means of the multidimensional code FLASH. Here, we present a series of 9 numerical simulations perfomed in two dimensions aimed at testing the possible influence of the initial perturbation (duration, strength, location, and size), the resolution adopted, or the size of the computational domain on the results. We show that results do not depend substantially on the specific choice of these parameters, demonstrating that Kelvin- Helmholtz instabilities can naturally lead to self-enrichment of the accreted envelope with core material, at levels that agree with observations. Comment: Accepted for publication in A&A
  12/2010;
• Source

  Available from: Priscilla Canizares

  Article: The LISA PathFinder DMU and Radiation Monitor

  Priscilla Canizares, Aleix Conchillo, Marc Diaz-Aguilo, Enrique Garcia-Berro, Lluis Gesa, Ferran Gibert, Catia Grimani, Ivan Lloro, Alberto Lobo, Ignacio Mateos, Miquel Nofrarias, Juan Ramos-Castro, Josep Sanjuan, Carlos F. Sopuerta
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  ABSTRACT: The LISA PathFinder DMU (Data Management Unit) flight model was formally accepted by ESA and ASD on 11 February 2010, after all hardware and software tests had been successfully completed. The diagnostics items are scheduled to be delivered by the end of 2010. In this paper we review the requirements and performance of this instrumentation, specially focusing on the Radiation Monitor and the DMU, as well as the status of their programmed use during mission operations, on which work is ongoing at the time of writing.
  09/2010;
• Conference Proceeding: Hardware implementation of the FAPEC lossless data compressor for space

  Alberto G. Villafranca, Shan Mignot, Jordi Portell, Enrique Garcia-Berro
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  ABSTRACT: The instruments used in modern space missions require increasing amounts of telemetry resources to download the acquired data to the ground. Data compression helps to mitigate this problem and, therefore, it is currently seen as a mandatory stage for most of the missions, although the available on-board processing power is often modest. In many cases, data compression must be performed without losses. FAPEC is a lossless data compression algorithm that typically offers better ratios than the CCSDS 121.0 recommendation on realistic data sets. Its compression efficiency is higher than 90% of the Shannon limit in most cases, even in presence of large amounts of noise and outliers. FAPEC has been successfully implemented in software and its low-complexity algorithm also seemed suitable for a hardware implementation. In this paper we describe a prototype FPGA implementation which has been developed targeting the antifuse radiation-hardened RTAX Actel family. We have assessed that FAPEC can be easily implemented in hardware without requiring an external memory. The prototype presents an initial throughput of 32 Mbit/s and a complexity of 120 Kgate, hence being a compact and a robust solution for generic lossless compression. Finally, we discuss potential improvements that could easily boost the performance beyond the barrier of 100 Mbit/s.
  Adaptive Hardware and Systems (AHS), 2010 NASA/ESA Conference on; 07/2010
• Source

  Available from: Enrique Garcia-Berro

  Article: New cooling sequences for old white dwarfs

  Isabel Renedo, Leandro G. Althaus, Marcelo M. Miller Bertolami, Alejandra D. Romero, Alejandro H. Corsico, Rene D. Rohrmann, Enrique Garcia-Berro
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  ABSTRACT: We present full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs. This is done by evolving white dwarf progenitors from the zero age main sequence, through the core hydrogen burning phase, the helium burning phase and the thermally pulsing asymptotic giant branch phase to the white dwarf stage. Complete evolutionary sequences are computed for a wide range of stellar masses and for two different metallicities: Z=0.01, which is representative of the solar neighborhood, and Z=0.001, which is appropriate for the study of old stellar systems, like globular clusters. During the white dwarf cooling stage we compute self-consistently the phase in which nuclear reactions are still important, the diffusive evolution of the elements in the outer layers and, finally, we also take into account all the relevant energy sources in the deep interior of the white dwarf, like the release of latent heat and the release of gravitational energy due to carbon-oxygen phase separation upon crystallization. We also provide colors and magnitudes for these sequences, based on a new set of improved non-gray white dwarf model atmospheres, which include the most up-to-date physical inputs like the Lyman alpha quasi-molecular opacity. The calculations are extended down to an effective temperature of 2,500 K. Our calculations provide a homogeneous set of evolutionary cooling tracks appropriate for mass and age determinations of old DA white dwarfs and for white dwarf cosmochronology of the different Galactic populations. Comment: 36 pages, 9 figures. Accepted for publication in The Astrophysical Journal
  05/2010;