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Title: THE C-FLAME QUENCHING BY CONVECTIVE BOUNDARY MIXING IN SUPER-AGB STARS AND THE FORMATION OF HYBRID C/O/Ne WHITE DWARFS AND SN PROGENITORS

After off-center C ignition in the cores of super asymptotic giant branch (SAGB) stars, the C flame propagates all the way down to the center, trailing behind it the C-shell convective zone, and thus building a degenerate ONe core. This standard picture is obtained in stellar evolution simulations if the bottom C-shell convection boundary is assumed to be a discontinuity associated with a strict interpretation of the Schwarzschild condition for convective instability. However, this boundary is prone to additional mixing processes, such as thermohaline convection and convective boundary mixing. Using hydrodynamic simulations, we show that contrary to previous results, thermohaline mixing is too inefficient to interfere with the C-flame propagation. However, even a small amount of convective boundary mixing removes the physical conditions required for the C-flame propagation all the way to the center. This result holds even if we allow for some turbulent heat transport in the CBM region. As a result, SAGB stars build in their interiors hybrid C-O-Ne degenerate cores composed of a relatively large CO core (M{sub CO} Almost-Equal-To 0.2 M{sub Sun }) surrounded by a thick ONe zone ({Delta}M{sub ONe} {approx}> 0.85 M{sub Sun }) with another thin CO layer above. If exposed by massmore » loss, these cores will become hybrid C-O-Ne white dwarfs. Otherwise, the ignition of C-rich material in the central core, surrounded by the thick ONe zone, may trigger a thermonuclear supernova (SN) explosion. The quenching of the C-flame may have implications for the ignition mechanism of SN Ia in the double-degenerate merger scenario.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6 (Canada)
  2. The Joint Institute for Nuclear Astrophysics, Notre Dame, IN 46556 (United States)
  3. Kavli Institute for Theoretical Physics and Department of Physics, Kohn Hall, University of California, Santa Barbara, CA 93106 (United States)
Publication Date:
OSTI Identifier:
22121868
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 772; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON MONOXIDE; CONVECTION; CONVECTIVE INSTABILITIES; EXPLOSIONS; FLAME PROPAGATION; QUENCHING; SCHWARZSCHILD METRIC; SIMULATION; STAR EVOLUTION; STELLAR WINDS; WHITE DWARF STARS