We present r-Java, an r-process code for open use that performs r-process nucleosynthesis calculations. Equipped with a simple graphical user interface, r-Java is capable of carrying out nuclear statistical equilibrium (NSE), as well as static and dynamic r-process calculations, for a wide range of input parameters. In this introductory paper, we present the motivation and details behind r-Java and results from our static and dynamic simulations. Static simulations are explored for a range of neutron irradiation and temperatures. Dynamic simulations are studied with a parameterized expansion formula. Our code generates the resulting abundance pattern based on a general entropy expression that can be applied to both degenerate and non-degenerate matter, allowing us to track the rapid density and temperature evolution of the ejecta during the initial stages of ejecta expansion. At present, our calculations are limited to the waiting-point approximation. We encourage the nuclear astrophysics community to provide feedback on the code and related documentation, which is available for download from the website of the Quark-Nova Project: http://quarknova.ucalgary.ca/.
Aims. We study a new mechanism for deflagration-to-detonation transition in thermonuclear supernovae (SNe Ia), based on the formation of shocks by amplification of sound waves in the steep density gradients of white dwarfs envelopes. We characterise, in terms of wavelength and amplitude, the perturbations which will ignite a detonation after their amplification. Methods. This study was performed using the well tested HERACLES code, a conservative hydrodynamical code, validated in the present specific application by an analytical description of the propagation of sound waves in white dwarfs. Thermonuclear combustion of the carbon oxygen fuel was treated with the α-chain nuclear reactions network.Results. In planar geometry we found the critical parameter to be the height of shock formation. When it occurs in the inner dense regions (ρ > 10 6 g cm −3 ) detonation is inevitable but can take an arbitrarily long time. We found that ignition can be achieved for perturbation as low as Mach number: M ∼ 0.005, with heating times compatible with typical explosion time scale (a few seconds). On the opposite no ignition occurs when shocks initiated by small amplitude or large wavelength form further away in less dense regions. We show finally that ignition is also achieved in a spherical self-gravitating spherical model of cold C+O white dwarf of 1.430 M , but due to the spherical damping of sound waves it necessitates stronger perturbation (M ∼ 0.02). Small perturbations (M ∼ 0.003) could still trigger detonation if a small helium layer is considered. In the context of SNe Ia, one has to consider further the initial expansion of the white dwarf, triggered by the deflagration, prior to the transition to detonation. As the star expands, gradients get flatter and ignition requires increasingly strong perturbations.
We study a new mechanism for deflagration to detonation transition in SN Ia, based on the formation of shocks by amplification of sound waves in the steep density gradients of white dwarfs. We characterize, in terms of wavelength and amplitude, the perturbations which will ignite a detonation after amplification. We found the critical parameter to be the height of shock formation. When it occurs in the inner dense regions (ρ > 10 6 g cm −3 ), detonation is inevitable but can take an arbitrarily long time. On the contrary no ignition occurs when shocks initiated by small amplitude or large wavelength perturbations form further away in less dense regions. We consider here a spherical self-gravitating model of a Chandrasekhar mass C+O white dwarf, with a steep density gradient near the envelope. For equimass C+O composition, detonation initiation requires a 2% velocity perturbation level corresponding to a Mach number M = 0.02. Small perturbations (M∼ 0.003) could however trigger detonations if a thin outer helium layer is considered.
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