A. Alexakis et al. 2004 ApJ 602 931 doi:10.1086/381086
On Heavy Element Enrichment in Classical Novae
FREEA. Alexakis1,2, A. C. Calder1,3, A. Heger1,4,5, E. F. Brown1,3, L. J. Dursi1,3, J. W. Truran1,3,4, R. Rosner1,2,3,4, D. Q. Lamb1,3,4, F. X. Timmes1,3, B. Fryxell1,4, M. Zingale6, P. M. Ricker7,8 and K. Olson1,9
Show affiliationsMany classical nova ejecta are enriched in CNO and Ne. Rosner and coworkers recently suggested that the enrichment might originate in the resonant interaction between large-scale shear flows in the accreted H/He envelope and gravity waves at the interface between the envelope and the underlying C/O white dwarf (WD). The shear flow amplifies the waves, which eventually form cusps and break. This wave breaking injects a spray of C/O into the superincumbent H/He. Using two-dimensional simulations, we formulate a quantitative expression for the amount of C/O per unit area that can be entrained, at saturation, into the H/He. The fraction of the envelope that is enriched depends on the horizontal distribution of shear velocity and the density contrast between the C/O WD and the H/He layer but is roughly independent of the vertical shape of the shear profile. Using this parameterization for the mixed mass, we then perform several one-dimensional Lagrangian calculations of an accreting WD envelope and consider two scenarios: that the wave breaking and mixing is driven by the convective flows and that the mixing occurs prior to the onset of convection. In the absence of enrichment prior to ignition, the base of the convective zone, as calculated from mixing-length theory with the Ledoux instability criterion, does not reach the C/O interface. As a result, there is no additional mixing, and the runaway is slow. In contrast, the formation of a mixed layer during the accretion of H/He, prior to ignition, causes a more violent runaway. The envelope can be enriched by 
25% of C/O by mass (consistent with that observed in some ejecta) for shear velocities, over the surface, with Mach numbers 0.4.
- Subject headings
hydrodynamics; methods: numerical; novae, cataclysmic variables; nuclear reactions, nucleosynthesis, abundances; waves
- Dates
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Issue 2 (2004 February 20)
Received 2003 July 3, accepted for publication 2003 October 28
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On Heavy Element Enrichment in Classical Novae
A. Alexakis et al. 2004 ApJ 602 931
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Low Mach Number Modeling of Type Ia Supernovae. I. Hydrodynamics
A. S. Almgren et al. 2006 ApJ 637 922
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The Response of Model and Astrophysical Thermonuclear Flames to Curvature and Stretch
L. J. Dursi et al. 2003 ApJ 595 955
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Propagation of the First Flames in Type Ia Supernovae
M. Zingale and L. J. Dursi 2007 ApJ 656 333
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On the Cellular Structure of Carbon Detonations
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Morphology of Rising Hydrodynamic and Magnetohydrodynamic Bubbles from Numerical Simulations
K. Robinson et al. 2004 ApJ 601 621
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Mapping Initial Hydrostatic Models in Godunov Codes
M. Zingale et al. 2002 ApJS 143 539
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FLASH: An Adaptive Mesh Hydrodynamics Code for Modeling Astrophysical Thermonuclear Flashes
B. Fryxell et al. 2000 ApJS 131 273
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Direct Numerical Simulations of Type Ia Supernovae Flames. II. The Rayleigh-Taylor Instability
J. B. Bell et al. 2004 ApJ 608 883
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On Validating an Astrophysical Simulation Code
A. C. Calder et al. 2002 ApJS 143 201