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Peer-reviewedCC BY 4.0The Astrophysical Journal

The Best Guess: Testing New and Old Formalisms for the Common Envelope against Observations

  • Riley Thai1
  • Amanda I. Karakas1
  • Zara Osborn1
  • Robert G. Izzard2
  • Ryosuke Hirai1,3
  • Alex J. Kemp4
  • Simon W. Campbell1
4 affiliations
  1. 1Monash University
  2. 2University of Surrey
  3. 3RIKEN Cluster for Pioneering Research (CPR)
  4. 4Institute of Astronomy (IvS)
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Abstract

We present a systematic test of formalisms for common envelope evolution by forward modeling observable post-common-envelope binaries (PCEBs). We compare predictions from the α -formalism and the Two-stage and SCATTER formalisms against observed PCEBs, including wide binaries with ultramassive white dwarfs and central binaries of planetary nebulae. The angular-momentum-based SCATTER formalism does not predict populations that match the complete observed population, even with adjustments to its parameters. We take this as indicative of fundamental challenges with using the orbital angular momentum balance to predict common envelope outcomes. The energy-based α - and hybrid Two-stage formalisms both well replicate the observed population. α CE ∼ 0.2–0.3 can match current observations, in agreement with previous works. Recombination energy is necessary, but only a fraction of it (∼10%–40%) can contribute in order to predict IK Peg–like binaries with ultramassive white dwarfs at the correct orbital periods. Our work suggests energy-based formalisms remain the most accurate for predicting common envelope outcomes, but more observations can constrain the recombination contribution and how these outcomes systematically vary with the donor mass.

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Cite

BibTeXRIS
BibTeX
@article{thai2026best,
  title = {{The Best Guess: Testing New and Old Formalisms for the Common Envelope against Observations}},
  author = {Riley Thai and Amanda I. Karakas and Zara Osborn and Robert G. Izzard and Ryosuke Hirai and Alex J. Kemp and Simon W. Campbell},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/ae9c3c},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae9c3c},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - The Best Guess: Testing New and Old Formalisms for the Common Envelope against Observations
AU  - Riley Thai
AU  - Amanda I. Karakas
AU  - Zara Osborn
AU  - Robert G. Izzard
AU  - Ryosuke Hirai
AU  - Alex J. Kemp
AU  - Simon W. Campbell
PY  - 2026
DA  - 2026/10/08
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/ae9c3c
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/ae9c3c
AB  - We present a systematic test of formalisms for common envelope evolution by forward modeling observable post-common-envelope binaries (PCEBs). We compare predictions from the α -formalism and the Two-stage and SCATTER formalisms against observed PCEBs, including wide binaries with ultramassive white dwarfs and central binaries of planetary nebulae. The angular-momentum-based SCATTER formalism does not predict populations that match the complete observed population, even with adjustments to its parameters. We take this as indicative of fundamental challenges with using the orbital angular momentum balance to predict common envelope outcomes. The energy-based α - and hybrid Two-stage formalisms both well replicate the observed population. α CE ∼ 0.2–0.3 can match current observations, in agreement with previous works. Recombination energy is necessary, but only a fraction of it (∼10%–40%) can contribute in order to predict IK Peg–like binaries with ultramassive white dwarfs at the correct orbital periods. Our work suggests energy-based formalisms remain the most accurate for predicting common envelope outcomes, but more observations can constrain the recombination contribution and how these outcomes systematically vary with the donor mass.
SN  - 0004-637X
SN  - 1538-4357
ER  -