Dynamical Formation of Close Binaries during the Pre-main-sequence Phase
AffiliationUniv Arizona, Steward Observ
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PublisherIOP PUBLISHING LTD
CitationDynamical Formation of Close Binaries during the Pre-main-sequence Phase 2018, 854 (1):44 The Astrophysical Journal
JournalThe Astrophysical Journal
Rights© 2018. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractSolar-type binaries with short orbital periods (P-close equivalent to 1-10. days; a less than or similar to 0.1. au) cannot form directly via fragmentation of molecular clouds or protostellar disks, yet their component masses are highly correlated, suggesting interaction during the pre-main-sequence (pre-MS) phase. Moreover, the close binary fraction of pre-MS stars is consistent with that of their MS counterparts in the field (F-close = 2.1%). Thus, we can infer that some migration mechanism operates during the early pre-MS phase (tau less than or similar to 5 Myr) that reshapes the primordial separation distribution. We test the feasibility of this hypothesis by carrying out a population synthesis calculation which accounts for two formation channels: Kozai-Lidov (KL) oscillations and dynamical instability in triple systems. Our models incorporate (1) more realistic initial conditions compared to previous studies, (2) octupole-level effects in the secular evolution, (3) tidal energy dissipation via weak-friction equilibrium tides at small eccentricities and via non-radial dynamical oscillations at large eccentricities, and (4) the larger tidal radius of a pre-MS primary. Given a 15% triple-star fraction, we simulate a close binary fraction from KL oscillations alone of F-close approximate to 0.4% after tau = 5. Myr, which increases to F-close 0.8% by tau = 5. Gyr. Dynamical ejections and disruptions of unstable coplanar triples in the disk produce solitary binaries with slightly longer periods P approximate to 10-100. days. The remaining approximate to 60% of close binaries with outer tertiaries, particularly those in compact coplanar configurations with log P-out (days) approximate to 2-5 (a(out) < 50 au), can be explained only with substantial extra energy dissipation due to interactions with primordial gas.
VersionFinal published version
SponsorsNASA's Einstein Postdoctoral Fellowship program [PF5-160139]