Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userType Ia Supernovae as Sites of p-process: Two-Dimensional Models Coupled to Nucleosynthesis
105
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We explore SNe Ia as p-process sites in the framework of two-dimensional SN Ia delayed detonation and pure deflagration models. The WD precursor is assumed to have reached the Chandrasekhar mass in a binary system by mass accretion from a giant/main sequence companion. We use enhanced s-seed distributions, obtained from a sequence of thermal pulse instabilities both in the AGB phase and in the accreted material. We apply the tracer-particle method to reconstruct the nucleosynthesis by the thermal histories of Lagrangian particles, passively advected in the hydrodynamic calculations. For each particle we follow the explosive nucleosynthesis with a detailed network for all isotopes up to 209Bi. We find that SNe Ia can produce a large amount of p-nuclei, both the light p-nuclei below A=120 and the heavy-p nuclei, at quite flat average production factors, tightly related to the s-process seed distribution. For the first time, we find a stellar source able to produce both, light and heavy p-nuclei almost at the same level as 56Fe, including the very debated neutron magic 92,94Mo and 96,98Ru. We also find that there is an important contribution from p-process nucleosynthesis to the s-only nuclei 80Kr, 86Sr, to the neutron magic 90Zr, and to the neutron-rich 96Zr. Finally, we investigate the metallicity effect on p-process. Starting with different s-process seed distributions, for two metallicities Z = 0.02 and Z = 0.001, running SNe Ia models with different initial composition, we estimate that SNe Ia can contribute to, at least, 50% of the solar p-process composition.
rate research
Read More
We present results for a suite of fourteen three-dimensional, high resolution hydrodynamical simulations of delayed-detonation modelsof Type Ia supernova (SN Ia) explosions. This model suite comprises the first set of three-dimensional SN Ia simulations with detailed isotopic yield information. As such, it may serve as a database for Chandrasekhar-mass delayed-detonation model nucleosynthetic yields and for deriving synthetic observables such as spectra and light curves. We employ a physically motivated, stochastic model based on turbulent velocity fluctuations and fuel density to calculate in situ the deflagration to detonation transition (DDT) probabilities. To obtain different strengths of the deflagration phase and thereby different degrees of pre-expansion, we have chosen a sequence of initial models with 1, 3, 5, 10, 20, 40, 100, 150, 200, 300, and 1600 (two different realizations) ignition kernels in a hydrostatic white dwarf with central density of 2.9 x 10^9 gcc, plus in addition one high central density (5.5 x 10^9 gcc), and one low central density (1.0 x 10^9 gcc) rendition of the 100 ignition kernel configuration. For each simulation we determined detailed nucleosynthetic yields by post-processing 10^6 tracer particles with a 384 nuclide reaction network. All delayed detonation models result in explosions unbinding the white dwarf, producing a range of 56Ni masses from 0.32 to 1.11 solar masses. As a general trend, the models predict that the stable neutron-rich iron group isotopes are not found at the lowest velocities, but rather at intermediate velocities (~3,000 - 10,000 km/s) in a shell surrounding a 56Ni-rich core. The models further predict relatively low velocity oxygen and carbon, with typical minimum velocities around 4,000 and 10,000 km/s, respectively.
We investigate whether pure deflagration models of Chandrasekhar-mass carbon-oxygen white dwarf stars can account for one or more subclass of the observed population of Type Ia supernova (SN Ia) explosions. We compute a set of 3D full-star hydrodynamic explosion models, in which the deflagration strength is parametrized using the multispot ignition approach. For each model, we calculate detailed nucleosynthesis yields in a post-processing step with a 384 nuclide nuclear network. We also compute synthetic observables with our 3D Monte Carlo radiative transfer code for comparison with observations. For weak and intermediate deflagration strengths (energy release E_nuc <~ 1.1 x 10^51 erg), we find that the explosion leaves behind a bound remnant enriched with 3 to 10 per cent (by mass) of deflagration ashes. However, we do not obtain the large kick velocities recently reported in the literature. We find that weak deflagrations with E_nuc ~ 0.5 x 10^51 erg fit well both the light curves and spectra of 2002cx-like SNe Ia, and models with even lower explosion energies could explain some of the fainter members of this subclass. By comparing our synthetic observables with the properties of SNe Ia, we can exclude the brightest, most vigorously ignited models as candidates for any observed class of SN Ia: their B - V colours deviate significantly from both normal and 2002cx-like SNe Ia and they are too bright to be candidates for other subclasses.
Among the major uncertainties involved in the Chandrasekhar mass models for Type Ia supernovae are the companion star of the accreting white dwarf (or the accretion rate that determines the carbon ignition density) and the flame speed after ignition. We present nucleosynthesis results from relatively slow deflagration (1.5 - 3 % of the sound speed) to constrain the rate of accretion from the companion star. Because of electron capture, a significant amount of neutron-rich species such as ^{54}Cr, ^{50}Ti, ^{58}Fe, ^{62}Ni, etc. are synthesized in the central region. To avoid the too large ratios of ^{54}Cr/^{56}Fe and ^{50}Ti/^{56}Fe, the central density of the white dwarf at thermonuclear runaway must be as low as ltsim 2 e9 gmc. Such a low central density can be realized by the accretion as fast as $dot M gtsim 1 times 10^{-7} M_odot yr^{-1}$. These rapidly accreting white dwarfs might correspond to the super-soft X-ray sources.
We present our first nucleosynthesis results from a numerical simulation of the thermonuclear disruption of a static cold Chandrasekhar-mass C/O white dwarf. The two-dimensional simulation was performed with an adaptive-mesh Eulerian hydrodynamics code, FLASH, that uses as a flame capturing scheme the evolution of a passive scaler. To compute the isotopic yields and their velocity distribution, 10,000 massless tracer particles are embedded in the star. The particles are advected along streamlines and provide a Lagrangian description of the explosion. We briefly describe our verification tests and preliminary results from post-processing the particle trajectories with a modest (214 isotopes) reaction network.
Various nucleosynthesis studies have pointed out that the r-process elements in very metal-poor (VMP) halo stars might have different origins. By means of familiar concepts from statistics (correlations, cluster analysis, rank tests of elemental abundances), we look for causally correlated elemental abundance patterns and attempt to link them to astrophysical events. Some of these events produce the r-process elements jointly with iron, while others do not have any significant iron contribution. In the early stage of our Galaxy, at least three r-process nucleosynthesis sites have been active. The first two produce and eject iron and the majority of the lighter r-process elements. We assign them to two different types of core-collapse events, not identical to regular core-collapse supernovae (CCSNe), which produce only light trans-Fe elements. The third category is characterized by a strong r-process and responsible for the major fraction of the heavy main r-process elements without a significant co-production of Fe. It does not appear to be connected to CCSNe, in fact the Fe found in the related r-process enriched stars must come from previously occurring CCSNe. The existence of actinide boost stars indicates a further division among strong r-process sites. We assign these two strong r-process sites to neutron star mergers without fast black hole formation and to events where the ejecta are dominated by black hole accretion disk outflows. Indications from the lowest-metallicity stars hint at a connection to massive single stars (collapsars) forming black holes in the early Galaxy.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
