White dwarf binaries suggest a common envelope efficiency α ∼ 1/3
Abstract
Common envelope (CE) evolution, which is crucial in creating short-period binaries and associated astrophysical events, can be constrained by reverse modelling of such binaries’ formation histories. Through analysis of a sample of well-constrained white dwarf (WD) binaries with low-mass primaries (seven eclipsing double WDs, two non-eclipsing double WDs, one WD-brown dwarf), we estimate the CE energy efficiency αCE needed to unbind the hydrogen envelope. We use grids of He- and CO-core WD models to determine the masses and cooling ages that match each primary WD’s radius and temperature. Assuming gravitational wave-driven orbital decay, we then calculate the associated ranges in post-CE orbital period. By mapping WD models to a grid of red giant progenitor stars, we determine the total envelope binding energies and possible orbital periods at the point CE evolution is initiated, thereby constraining αCE. Assuming He-core WDs with progenitors of 0.9–2.0 M⊙, we find αCE ∼ 0.2–0.4 is consistent with each system we model. Significantly higher values of αCE are required for higher mass progenitors and for CO-core WDs, so these scenarios are deemed unlikely. Our values are mostly consistent with previous studies of post-CE WD binaries, and they suggest a nearly constant and low envelope ejection efficiency for CE events that produce He-core WDs.
Copyright and License
Acknowledgement
We are grateful for support from the NSF through grant AST-2205974. JF is thankful for support through an Innovator Grant from The Rose Hills Foundation, and the Sloan Foundation through grant FG-2018-10515. We thank Sterl Phinney and Kevin Burdge for useful discussions. We thank the anonymous referee for their useful feedback and suggestions.
Funding
We are grateful for support from the NSF through grant AST-2205974. JF is thankful for support through an Innovator Grant from The Rose Hills Foundation, and the Sloan Foundation through grant FG-2018-10515.
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Additional details
- National Science Foundation
- AST-2205974
- Rose Hills Foundation
- Alfred P. Sloan Foundation
- FG-2018-10515
- Accepted
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2022-11-01Accepted
- Available
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2022-11-18Published
- Available
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2022-12-05Corrected and typeset
- Caltech groups
- Astronomy Department, TAPIR, Walter Burke Institute for Theoretical Physics
- Publication Status
- Published