2017/06/30 by Maxwell Moe, Kaitlin M. Kratter · 1 citation
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Binary number #Binary star #Dissipation #Instability #Molecular cloud #Population #RADIUS #Stars #Stellar, planetary, and galactic studies #Tidal force #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/aaa6d2
Accepted by ApJ; 23 pages; 8 figures; this version incorporates changes made to address comments by referee
openalex created_date 2017/07/14 · arxiv created 2018/01/26 · openalex publication_date 2018/02/09 · arxiv updated 2018/02/21 · openalex updated_date 2026/08/06
Abstract Solar-type binaries with short orbital periods ( days; a ≲ 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 ( ). Thus, we can infer that some migration mechanism operates during the early pre-MS phase ( τ ≲ 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 after τ = 5 Myr, which increases to by τ = 5 Gyr. Dynamical ejections and disruptions of unstable coplanar triples in the disk produce solitary binaries with slightly longer periods P ≈ 10–100 days. The remaining ≈60% of close binaries with outer tertiaries, particularly those in compact coplanar configurations with log (days) ≈ 2–5 ( au), can be explained only with substantial extra energy dissipation due to interactions with primordial gas.