The Formation of Very Close Binary Stars

Abstract

The majority of very close binaries (orbital periods P < 5 days) are in triples. Previous studies surmised that the tertiary hardened the inner binary via Kozai–Lidov cycles coupled with tidal friction. Alternatively, the trend could be due to a common origin, e.g., more massive molecular cores and protostellar disks are more likely to fragment twice into a triple and harden the inner binary to very short periods via disk migration. Disk migration occurs during the embedded Class I protostellar phase while secular evolution with a tertiary occurs on much longer timescales. To determine the dominant migration mechanism, I accurately measure the very close binary fractions of both late-type and early-type primaries in star-forming environments. After combining five surveys, the late-type Class II/III T Tauri very close binary fraction is F VCB = 2.1 − 0.5 + 1.0 %, which is consistent with the measurement for late-type field main-sequence (MS) stars (1.7% ± 0.1%). More than 85% of very close late-type binaries hardened via disk migration during the Class I protostellar phase. I next measure the OGLE-III eclipsing binary (EB) fractions of young massive stars in the LMC. The very close EB fractions of massive young stellar objects (YSOs; F VCEB = 8.3 − 3.2 + 4.9 %), OB stars near massive YSOs (4.7% ± 0.8%), and OB stars in small, young H II regions (6.4% ± 1.5%) are consistent with each other and the measurement for OB stars in slightly older clusters (4.7% ± 0.3%). More than 90% of very close massive binaries hardened via disk migration during the embedded protostellar phase.

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Cite

BibTeX RIS

BibTeX

@article{moe2026formation,
  title = {{The Formation of Very Close Binary Stars}},
  author = {Maxwell Moe},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea147},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea147},
  note = {CC BY 4.0},
}

RIS

TY  - JOUR
TI  - The Formation of Very Close Binary Stars
AU  - Maxwell Moe
PY  - 2026
DA  - 2026/10/14
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea147
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea147
AB  - The majority of very close binaries (orbital periods P < 5 days) are in triples. Previous studies surmised that the tertiary hardened the inner binary via Kozai–Lidov cycles coupled with tidal friction. Alternatively, the trend could be due to a common origin, e.g., more massive molecular cores and protostellar disks are more likely to fragment twice into a triple and harden the inner binary to very short periods via disk migration. Disk migration occurs during the embedded Class I protostellar phase while secular evolution with a tertiary occurs on much longer timescales. To determine the dominant migration mechanism, I accurately measure the very close binary fractions of both late-type and early-type primaries in star-forming environments. After combining five surveys, the late-type Class II/III T Tauri very close binary fraction is F VCB = 2.1 − 0.5 + 1.0 %, which is consistent with the measurement for late-type field main-sequence (MS) stars (1.7% ± 0.1%). More than 85% of very close late-type binaries hardened via disk migration during the Class I protostellar phase. I next measure the OGLE-III eclipsing binary (EB) fractions of young massive stars in the LMC. The very close EB fractions of massive young stellar objects (YSOs; F VCEB = 8.3 − 3.2 + 4.9 %), OB stars near massive YSOs (4.7% ± 0.8%), and OB stars in small, young H II regions (6.4% ± 1.5%) are consistent with each other and the measurement for OB stars in slightly older clusters (4.7% ± 0.3%). More than 90% of very close massive binaries hardened via disk migration during the embedded protostellar phase.
SN  - 0004-637X
SN  - 1538-4357
ER  -

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