Novae: The Evolution from Onset of Convection to the Runaway

Glasner, S. Ami; Livne, Eli; Truran, J. W.

doi:10.1086/519234

Cited by 32 publications

(47 citation statements)

References 22 publications

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“…The mass-averaged CNO abundance in the envelope reached ∼0.206 at the end of this simulation, close to the value found for model A. These results confirm that 800 km is an appropriate choice for the width of the computational domain, stressing that above a threshold value the course of the TNR is insensitive to the adopted width, in agreement with the sensitivity study performed by Glasner et al (2007).…”

Section: Effect Of the Size Of The Computational Domainsupporting

confidence: 89%

“…All simulations discussed so far (e.g., models A to G) were performed with a resolution of 1.56 × 1.56 km, a value similar to the minimum resolutions adopted in Glasner et al (2007) which is roughly ∼1.4 × 1.4 km, and in Kercek et al (1998), 1 × 2 km. To quantitatively assess the possible effect of the resolution, two additional test cases were computed with exactly the same input parameters as in model A but with two different resolutions: 1 × 1 km (model H) and 0.39 × 0.39 km (model I) 3 .…”

Section: Effect Of the Grid Resolutionmentioning

confidence: 99%

“…Several mechanisms have been proposed, including diffusion-induced mixing (Prialnik & Kovetz 1984;Kovetz & Prialnik 1985;Iben et al 1991Iben et al , 1992, shear mixing at the disk-envelope interface (Durisen 1977;Kippenhahn & Thomas 1978;MacDonald 1983;Livio & Truran 1987;, convective overshoot-induced flame propagation (Woosley 1986), and mixing by gravity wave breaking on the white dwarf surface (Rosner et al 2001;Alexakis et al 2004). The multidimensional nature of mixing has been addressed by Glasner & Livne (1995) and Glasner et al (1997Glasner et al ( , 2005Glasner et al ( , 2007 with 2-D simulations of CO-novae performed with VULCAN, an arbitrarily Lagrangian Eulerian (ALE) hydrocode capable of handling both explicit and implicit steps. They report an effective mixing triggered by Kelvin-Helmholtz instabilities that produced metallicity enhancements to levels in agreement with observations.…”

Section: Introductionmentioning

confidence: 99%

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Mixing in classical novae: a 2-D sensitivity study

Casanova

José

Garcı́a–Berro

et al. 2011

A&A

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Context. 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) × 10 8 K. During these events, about 10 −4 −10 −5 M , 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. Aims. 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. Methods. 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. Results. We show that results do not depend substantially on the specific choice of these parameters, demonstrating that KelvinHelmholtz instabilities can naturally lead to self-enrichment of the accreted envelope with core material, at levels that agree with observations.

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Section: Effect Of the Size Of The Computational Domainsupporting

confidence: 89%

Section: Effect Of the Grid Resolutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mixing in classical novae: a 2-D sensitivity study

Casanova

José

Garcı́a–Berro

et al. 2011

A&A

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“…The energy release in the white dwarf envelope through thermonuclear burning computed in 1D numerical simulations with convective motions described by the mixing-length theory allows high envelope expansion velocities to be obtained (see, e.g., Starrfield et al 1985;Prialnik 1986; Yaron et al, 2005). However, more detailed 2D and 3D burning calculations do not allow such high velocities to be obtained without the assumptions about greatly enhanced carbon and oxygen abundances in the envelope (Kercek et al 1998; Glasner et al 2005Glasner et al , 2007. Measuring the envelope expansion law would be the most important observational test of the white dwarf envelope burning model.…”

Section: Introduction X-ray Emission During Classical Nova Outburstsmentioning

confidence: 99%

Diagnostics of the early explosion phase of a classical nova using its X-ray emission: A model for the X-ray outburst of CI Camelopardalis in 1998

2008

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Abstract-We have computed a spherically symmetric model for the interaction of matter ejected during the outburst of a classical nova with the stellar wind from its optical component. This model is used to describe the intense X-ray outburst (the peak 3-20 keV flux was ∼2 Crab) of the binary system CI Camelopardalis in 1998. According to our model, the stellar wind from the optical component heated by a strong shock wave produced when matter is ejected from the white dwarf as the result of a thermonuclear explosion on its surface is the emission source in the standard X-ray band. Comparison of the calculated and observed time dependences of the mean radiation temperature and luminosity of the binary system during its outburst has yielded very important characteristics of the explosion. We have been able to measure the velocity of the ejected matter immediately after the onset of the explosion for the first time: it follows from our model that the ejected matter had a velocity of ∼2700 km s −1 even on 0.1-0.5 day after the outburst onset and it flew with such a velocity for the first 1-1.5 day under an external force, possibly, the radiation pressure from the white dwarf. Subsequently, the matter probably became transparent and began to decelerate. The time dependence of the mean radiation temperature at late expansion phases has allowed us to estimate the mass of the ejected matter, ∼10 −7 -10 −6 M . The mass loss rate in the stellar wind required to explain the observed peak luminosity of the binary system during its outburst has been estimated to beṀ ∼ (1 − 2) × 10 −6 M yr −1 .PACS numbers : 97.30.Qt; 97.80.Gm; 95.30.Lz

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“…Especially challenging instances of wave-propagationrelated stiffness are encountered in the flows of the simmering and ignition phase of classical novae (Kercek et al 1999;Glasner et al 2007), X-ray bursts (Lin et al 2006), and Type Ia supernovae (Höflich & Stein 2002;Zingale et al 2009). These flows are initially deeply subsonic, but due to energy release by thermonuclear runaway processes, they evolve to become transonic or even supersonic.…”

Section: Introductionmentioning

confidence: 99%

On multigrid solution of the implicit equations of hydrodynamics

Kifonidis

Müller

2012

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Aims. We describe and study a family of new multigrid iterative solvers for the multidimensional, implicitly discretized equations of hydrodynamics. Schemes of this class are free of the Courant-Friedrichs-Lewy condition. They are intended for simulations in which widely differing wave propagation timescales are present. A preferred solver in this class is identified. Applications to some simple stiff test problems that are governed by the compressible Euler equations, are presented to evaluate the convergence behavior, and the stability properties of this solver. Algorithmic areas are determined where further work is required to make the method sufficiently efficient and robust for future application to difficult astrophysical flow problems. Methods. The basic equations are formulated and discretized on non-orthogonal, structured curvilinear meshes. Roe's approximate Riemann solver and a second-order accurate reconstruction scheme are used for spatial discretization. Implicit Runge-Kutta (ESDIRK) schemes are employed for temporal discretization. The resulting discrete equations are solved with a full-coarsening, nonlinear multigrid method. Smoothing is performed with multistage-implicit smoothers. These are applied here to the time-dependent equations by means of dual time stepping. Results. For steady-state problems, our results show that the efficiency of the present approach is comparable to the best implicit solvers for conservative discretizations of the compressible Euler equations that can be found in the literature. The use of red-black as opposed to symmetric Gauss-Seidel iteration in the multistage-smoother is found to have only a minor impact on multigrid convergence. This should enable scalable parallelization without having to seriously compromise the method's algorithmic efficiency. For time-dependent test problems, our results reveal that the multigrid convergence rate degrades with increasing Courant numbers (i.e. time step sizes). Beyond a Courant number of nine thousand, even complete multigrid breakdown is observed. Local Fourier analysis indicates that the degradation of the convergence rate is associated with the coarse-grid correction algorithm. An implicit scheme for the Euler equations that makes use of the present method was, nevertheless, able to outperform a standard explicit scheme on a time-dependent problem with a Courant number of order 1000. Conclusions. For steady-state problems, the described approach enables the construction of parallelizable, efficient, and robust implicit hydrodynamics solvers. The applicability of the method to time-dependent problems is presently restricted to cases with moderately high Courant numbers. This is due to an insufficient coarse-grid correction of the employed multigrid algorithm for large time steps. Further research will be required to help us to understand and overcome the observed multigrid convergence difficulties for time-dependent problems.

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Novae: The Evolution from Onset of Convection to the Runaway

Cited by 32 publications

References 22 publications

Mixing in classical novae: a 2-D sensitivity study

Mixing in classical novae: a 2-D sensitivity study

Diagnostics of the early explosion phase of a classical nova using its X-ray emission: A model for the X-ray outburst of CI Camelopardalis in 1998

On multigrid solution of the implicit equations of hydrodynamics

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