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Search Results: 1 - 10 of 366960 matches for " P. Lorén-Aguilar "
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Smoothed Particle Hydrodynamics simulations of white dwarf collisions and close encounters
P. Lorén-Aguilar,J. Isern,E. García-Berro
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.16878.x
Abstract: The collision of two white dwarfs is a quite frequent event in dense stellar systems, like globular clusters and galactic nuclei. In this paper we present the results of a set of simulations of the close encounters and collisions of two white dwarfs. We use an up- to-date smoothed particle hydrodynamics code that incorporates very detailed input physics and an improved treatment of the artificial viscosity. Our simulations have been done using a large number of particles (~ 4 \times 10^5) and covering a wide range of velocities and initial distances of the colliding white dwarfs. We discuss in detail when the initial eccentric binary white dwarf survives the closest approach, when a lateral collision in which several mass transfer episodes occur is the outcome of the newly formed binary system, and which range of input parameters leads to a direct collision, in which only one mass transfer episode occurs. We also discuss the characteristics of the final configuration and we assess the possible observational signatures of the merger, such as the associated gravitational waveforms and the fallback luminosities. We find that the overall evolution of the system and the main characteristics of the final object agree with those found in previous studies. We also find that the fallback luminosities are close to 10^48 erg/s. Finally, we find as well that in the case of lateral and direct collisions the gravitational waveforms are characterized by large-amplitude peaks which are followed by a ring-down phase, while in the case in which the binary white dwarf survives the closest approach, the gravitational pattern shows a distinctive behavior, typical of eccentric systems.
High-resolution Smoothed Particle Hydrodynamics simulations of the merger of binary white dwarfs
P. Lorén-Aguilar,J. Isern,E. García-Berro
Physics , 2009, DOI: 10.1063/1.3141311
Abstract: We present the results of a set of high-resolution simulations of the merging process of two white dwarfs. In order to do so, we use an up-to-date Smoothed Particle Hydrodynamics code which incorporates very detailed input physics and an improved treatment of the artificial viscosity. Our simulations have been done using a large number of particles (4x10^5) and cover the full range of masses and chemical compositions of the coalescing white dwarfs. We also compare the time evolution of the system during the first phases of the coalescence with that obtained using a simplified treatment of mass transfer, we discuss in detail the characteristics of the final configuration, we assess the possible observational signatures of the merger, like the associated gravitational waveforms and the fallback X-ray flares, and we study the long-term evolution of the coalescence.
Type Ia supernovae and the DD scenario
J. Isern,E. García-Berro,P. Lorén-Aguilar
Physics , 2011,
Abstract: Type Ia supernovae are thought to be the outcome of the thermonuclear explosion of a white dwarf in a close binary system. Two possible scenarios, not necessarily incompatible, have been advanced. One assumes a white dwarf that accretes matter from a nondegenerate companion (the single degenerate scenario), the other assumes two white dwarfs that merge as a consequence of the emission of gravitational waves (the double degenerate scenario). The delay time distribution of star formation bursts strongly suggests that the DD scenario should be responsible of the late time explosions, but this contradicts the common wisdom that the outcome of the merging of two white dwarfs is an accretion induced collapse to a neutron star. In this contribution we review some of the most controversial issues of this problem.
Smoothed Particle Hydrodynamics simulations of the core-degenerate scenario for Type Ia supernovae
G. Aznar-Siguán,E. García-Berro,P. Lorén-Aguilar,N. Soker,A. Kashi
Physics , 2015, DOI: 10.1093/mnras/stv824
Abstract: The core-degenerate (CD) scenario for type Ia supernovae (SN Ia) involves the merger of the hot core of an asymptotic giant branch (AGB) star and a white dwarf, and might contribute a non-negligible fraction of all thermonuclear supernovae. Despite its potential interest, very few studies, and based on only crude simplifications, have been devoted to investigate this possible scenario, compared with the large efforts invested to study some other scenarios. Here we perform the first three-dimensional simulations of the merger phase, and find that this process can lead to the formation of a massive white dwarf, as required by this scenario. We consider two situations, according to the mass of the circumbinary disk formed around the system during the final stages of the common envelope phase. If the disk is massive enough, the stars merge on a highly eccentric orbit. Otherwise, the merger occurs after the circumbinary disk has been ejected and gravitational wave radiation has brought the stars close to the Roche lobe radius on a nearly circular orbit. Not surprisingly, the overall characteristics of the merger remnants are similar to those found for the double-degenerate (DD) scenario, independently of the very different core temperature and of the orbits of the merging stars. They consist of a central massive white dwarf, surrounded by a hot, rapidly rotating corona and a thick debris region.
On the possible observational signatures of white dwarf dynamical interactions
G. Aznar-Siguán,E. García-Berro,M. Magnien,P. Lorén-Aguilar
Physics , 2014, DOI: 10.1093/mnras/stu1309
Abstract: We compute the possible observational signatures of white dwarf dynamical interactions in dense stellar environments. Specifically, we compute the emission of gravitational waves, and we compare it with the sensitivity curves of planned space-borne gravitational wave detectors. We also compute the light curves for those interactions in which a detonation occurs, and one of the stars is destroyed, as well as the corresponding neutrino luminosities. We find that for the three possible outcomes of these interactions - which are the formation of an eccentric binary system, a lateral collision in which several mass transfer episodes occur, and a direct one in which just a single mass transfer episode takes place - only those in which an eccentric binary are formed are likely to be detected by the planned gravitational wave mission eLISA, while more sensitive detectors would be able to detect the signals emitted in lateral collisions. On the other hand, the light curves (and the thermal neutrino emission) of these interactions are considerably different, producing both very powerful outbursts and low luminosity events. Finally, we also calculate the X-ray signature produced in the aftermath of those interactions for which a merger occurs. We find that the temporal evolution follows a power law with the same exponent found in the case of the mergers of two neutron stars, although the total energy released is smaller.
Nucleosynthesis during the Merger of White Dwarfs and the Origin of R Coronae Borealis Stars
R. Longland,P. Lorén-Aguilar,J. José,E. García-Berro,L. G. Althaus,J. Isern
Physics , 2011, DOI: 10.1088/2041-8205/737/2/L34
Abstract: Many hydrogen deficient stars are characterised by surface abundance patterns that are hard to reconcile with conventional stellar evolution. Instead, it has been suggested that they may represent the result of a merger episode between a helium and a carbon-oxygen white dwarf. In this Letter, we present a nucleosynthesis study of the merger of a 0.4 M_sol helium white dwarf with a 0.8 M_sol carbon-oxygen white dwarf, by 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.
White dwarf mergers and the origin of R Coronae Borealis stars
P. Lorén-Aguilar,R. Longland,J. José,E. García-Berro,L. G. Althaus,J. Isern
Physics , 2011,
Abstract: We present a nucleosynthesis study of the merger of a 0.4 solar masses helium white dwarf with a 0.8 solar masses 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.
Double degenerate mergers as progenitors of high-field magnetic white dwarfs
E. García-Berro,P. Lorén-Aguilar,G. Aznar-Siguán,S. Torres,J. Camacho,L. G. Althaus,A. H. Córsco,B. Külebi,J. Isern
Physics , 2012, DOI: 10.1088/0004-637X/749/1/25
Abstract: High-field magnetic white dwarfs have been long suspected to be the result of stellar mergers. However, the nature of the coalescing stars and the precise mechanism that produces the magnetic field are still unknown. Here we show that the hot, convective, differentially rotating corona present in the outer layers of the remnant of the merger of two degenerate cores is able to produce magnetic fields of the required strength that do not decay for long timescales. We also show, using an state-of-the-art Monte Carlo simulator, that the expected number of high-field magnetic white dwarfs produced in this way is consistent with that found in the Solar neighborhood.
On the origin of high-field magnetic white dwarfs
E. García-Berro,S. Torres,P. Lorén-Aguilar,G. Aznar-Siguán,J. Camacho,B. Külebi,J. Isern,L. G. Althaus,A. H. Córsico
Physics , 2012,
Abstract: High-field magnetic white dwarfs have been long suspected to be the result of stellar mergers. However, the nature of the coalescing stars and the precise mechanism that produces the magnetic field are still unknown. Here we show that the hot, convective, differentially rotating corona present in the outer layers of the remnant of the merger of two degenerate cores is able to produce magnetic fields of the required strength that do not decay for long timescales. We also show, using an state-of-the-art Monte Carlo simulator, that the expected number of high-field magnetic white dwarfs produced in this way is consistent with that found in the solar neighborhood.
Detonations in white dwarf dynamical interactions
Gabriela Aznar-Siguán,Enrique García-Berro,Pablo Lorén-Aguilar,Jordi José,Jordi Isern
Physics , 2013, DOI: 10.1093/mnras/stt1198
Abstract: In old, dense stellar systems collisions of white dwarfs are a rather frequent phenomenon. Here we present the results of a comprehensive set of Smoothed Particle Hydrodynamics simulations of close encounters of white dwarfs aimed to explore the outcome of the interaction and the nature of the final remnants for different initial conditions. Depending on the initial conditions and the white dwarf masses, three different outcomes are possible. Specifically, the outcome of the interaction can be either a direct or a lateral collision or the interaction can result in the formation of an eccentric binary system. In those cases in which a collision occurs, the infalling material is compressed and heated such that the physical conditions for a detonation may be reached during the most violent phases of the merger. While we find that detonations occur in a significant number of our simulations, in some of them the temperature increase in the shocked region rapidly lifts degeneracy, leading to the quenching of the burning. We thus characterize under which circumstances a detonation is likely to occur as a result of the impact of the disrupted star on the surface of the more massive white dwarf. Finally, we also study which interactions result in bound systems, and in which ones the more massive white dwarf is also disrupted as a consequence of the dynamical interaction. The sizable number of simulations performed in this work allows to find how the outcome of the interaction depends on the distance at closest approach, and on the masses of the colliding white dwarfs, and which is the chemical pattern of the nuclearly processed material. Finally, we also discuss the influence of the masses and core chemical compositions of the interacting white dwarfs and the different kinds of impact in the properties of the remnants.
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