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Convection in common envelopes and the formation of double white dwarfs

Published online by Cambridge University Press:  09 October 2020

E. C. Wilson
Affiliation:
Center for Computational Relativity and Gravitation, Rochester Institute of Technology, NY14623, USA email: [email protected]
J. Nordhaus
Affiliation:
Center for Computational Relativity and Gravitation, Rochester Institute of Technology, NY14623, USA email: [email protected] National Technical Institute for the Deaf, Rochester Institute of Technology, NY14623, USA email: [email protected]
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Abstract

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Formation of close double white dwarfs likely requires the initial binary system to evolve through two successive common envelope (CE) phases. A prominent method for describing CE outcomes involves defining an ejection efficiency, αeff, which quantifies the fraction of orbital energy available to unbind the envelope. Reproducing observed post-CE orbital parameters has proven difficult for numerical simulations, as the companion’s decaying orbit fails to eject the envelope. The ejection failure seen in numerical simulations may be resolved with a proper treatment of convection, whereby the binary orbit shrinks before energy can drive ejection. Where the orbital decay timescale exceeds the convective transport timescale, the energy released during inspiral is carried to the stellar surface and radiated away. By including convection, we produce sub-day post-CE orbital periods, a result consistent with observations. We comment on the effects of convection for the population of double white dwarfs that evolve through two CEs.

Type
Contributed Papers
Copyright
© International Astronomical Union 2020

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