On heavy element enrichment in classical novae

A. Alexakis, A. C. Calder, A. Heger, E. F. Brown, L. J. Dursi, J. W. Truran, R. Rosner, D. Q. Lamb, F. X. Timmes, B. Fryxell, M. Zingale, P. M. Ricker, K. Olson

Research output: Contribution to journalArticle

49 Scopus citations

Abstract

Many 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.

Original languageEnglish (US)
Pages (from-to)931-937
Number of pages7
JournalAstrophysical Journal
Volume602
Issue number2 I
DOIs
StatePublished - Feb 20 2004
Externally publishedYes

Keywords

  • Hydrodynamics
  • Methods: numerical
  • Novae, cataclysmic variables
  • Nuclear reactions, Nucleosynthesis, abundances
  • Waves

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Alexakis, A., Calder, A. C., Heger, A., Brown, E. F., Dursi, L. J., Truran, J. W., Rosner, R., Lamb, D. Q., Timmes, F. X., Fryxell, B., Zingale, M., Ricker, P. M., & Olson, K. (2004). On heavy element enrichment in classical novae. Astrophysical Journal, 602(2 I), 931-937. https://doi.org/10.1086/381086