Low mach number modeling of type i x-ray burst deflagrations

David J. Lin*, Alvin Bayliss, Ronald E. Taam

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

The low Mach number approximation (LMNA) is applied to two-dimensional hydrodynamic modeling of type I X-ray bursts on a rectangular patch on the surface of a nonrotating neutron star. Because such phenomena involve decidedly subsonic flows, the time step increase offered by the LMNA makes routine simulations of these deflagrations feasible in an environment where strong gravity produces significant stratification, while allowing for potentially significant lateral differences in temperature and density. The model is employed to simulate the heating, peak, and initial cooling stages in the deep envelope layers of a burst. During the deflagration, Bénard-like cells naturally fill up a vertically expanding convective layer. The Mach number is always less than 0.15 throughout the simulation, thus justifying the low Mach number approximation. While the convective layer is superadiabatic on average, significant fluctuations in adiabaticity occur within it on subconvective timescales. Due to convective layer expansion, significant compositional mixing naturally occurs, but tracer particle penetration through the convective layer boundaries on convective timescales is temporary and spatially limited. Thus, mixing occurs on the relatively slow burst timescale through thermal expansion of the convective layer rather than from mass penetration of the convective layer boundary through particle convection. At the convective layer boundaries where mixing is less efficient, the actual temperature gradient more closely follows the Ledoux criterion.

Original languageEnglish (US)
Pages (from-to)545-557
Number of pages13
JournalAstrophysical Journal
Volume653
Issue number1 I
DOIs
StatePublished - Dec 10 2006

Keywords

  • Convection
  • Hydrodynamics
  • Methods: numerical
  • Stars: neutron
  • X-rays: bursts

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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