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Kelvin–Helmholtz instabilities as the source of inhomogeneous mixing in nova explosions

Nature volume 478, pages 490–492 (2011)Cite this article

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Abstract

Classical novae1,2 are thermonuclear explosions in binary stellar systems containing a white dwarf accreting material from a close companion star. They repeatedly eject 10−4–10−5 solar masses of nucleosynthetically enriched gas into the interstellar medium, recurring on intervals of decades to tens of millennia. They are probably the main sources3,4 of Galactic 15N, 17O and 13C. The origin of the large enhancements and inhomogeneous distribution of these species observed in high-resolution spectra5 of ejected nova shells has, however, remained unexplained for almost half a century6. Several mechanisms7, including mixing by diffusion8, shear9 or resonant gravity waves10, have been proposed in the framework of one-dimensional or two-dimensional simulations, but none has hitherto proven successful because convective mixing can only be modelled accurately in three dimensions. Here we report the results of a three-dimensional nuclear-hydrodynamic simulation of mixing at the core–envelope interface during nova outbursts. We show that buoyant fingering drives vortices from the Kelvin–Helmholtz instability, which inevitably enriches the accreted envelope with material from the outer white-dwarf core. Such mixing also naturally produces large-scale chemical inhomogeneities. Both the metallicity enhancement and the intrinsic dispersions in the abundances are consistent with the observed values.

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Figure 1: Mixing driven by Kelvin–Helmholtz instabilities.
Figure 2: Cumulant distributions.

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Acknowledgements

The software used in this work was developed in part by the Department of Energy-supported Alliances Center for Astrophysical Thermonuclear Flashes at the University of Chicago. This work was partly supported by Spanish Ministerio de Educación y Ciencia grants, by the Agència de Gestió d'Ajuts Universitaris i de Recerca of the Generalitat de Catalunya, by the E.U. European Fund for Regional Development, and by the European Science Foundation EUROCORES Program EuroGENESIS. We also acknowledge the Barcelona Supercomputing Center for allocation of time at the MareNostrum supercomputer.

Author information

Authors and Affiliations

  1. Departament de Física i Enginyeria Nuclear, EUETIB, Universitat Politècnica de Catalunya, C./ Comte d’Urgell 187, E-08036 Barcelona, Spain

    Jordi Casanova & Jordi José

  2. Institut d’Estudis Espacials de Catalunya, Ed. Nexus-201, C./ Gran Capità 2-4, E-08034 Barcelona, Spain

    Jordi Casanova, Jordi José & Enrique García-Berro

  3. Departament de Física Aplicada, Universitat Politècnica de Catalunya, C./ Esteve Terrades 5, E-08860 Castelldefels (Barcelona), Spain

    Enrique García-Berro

  4. Dipartimento di Fisica ‘Enrico Fermi’, Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy

    Steven N. Shore

  5. Department of Physics and Astronomy, Stony Brook University, Stony Brook, 11794-3800, New York, USA

    Alan C. Calder

Authors
  1. Jordi Casanova
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  2. Jordi José
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  3. Enrique García-Berro
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  4. Steven N. Shore
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  5. Alan C. Calder
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Contributions

All authors contributed equally to the results presented here.

Corresponding author

Correspondence to Jordi José.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text, which describes Supplementary Movies 1 and 2. This file was replaced on 14 November 2011. (PDF 40 kb)

Supplementary Movie 1

This movie shows a two-dimensional slice of the time evolution of the 12C abundance, in logarithmic scale, at the core-envelope interface during a nova outburst on a 1 solar mass CO white dwarf that accretes solar composition matter. (MOV 25326 kb)

Supplementary Movie 2

This movie shows a two-dimensional slice of the time evolution of the 15O abundance, in linear scale, at the core-envelope interface during a nova outburst on a 1 solar mass CO white dwarf that accretes solar composition matter. (MOV 25362 kb)

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Casanova, J., José, J., García-Berro, E. et al. Kelvin–Helmholtz instabilities as the source of inhomogeneous mixing in nova explosions. Nature 478, 490–492 (2011). https://doi.org/10.1038/nature10520

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