The mystery in Gaia DR3 triples: occurrence rates, orientations, and eccentricities of wide tertiaries around close binaries

Abstract

The formation of close binaries has been an open question for decades. A large fraction of close binaries are in triple systems, suggesting that their formation may be associated with the Kozai-Lidov mechanism. However, this picture remains under debate because the configurations of many observed triples are unlikely to trigger the Kozai-Lidov mechanism. In this paper, we use the close binary samples, including eclipsing, spectroscopic, and astrometric binaries, from Gaia Data Release 3 to investigate the mysterious connection between inner binaries and their wide tertiaries. We show that the wide tertiary (at $10^3$-$10^4$ AU) fraction increases with decreasing orbital periods of the inner binaries. The wide tertiary fraction of eclipsing binaries (a median orbital period of $0.41$ day) is $2.33\pm 0.11$ times higher than the field wide binary fraction. Furthermore, there is a tentative excess at $\sim 10^4$ AU for tertiaries of eclipsing binaries. Using the $v$-$r$ angle distributions, we show that wide tertiaries have isotropic orientations with respect to the inner binaries, and the co-planar orbits can be ruled out. The inferred eccentricity distribution of wide tertiaries is consistent ($<1\sigma$) with being thermal ($f(e)\propto e$), similar to wide binaries at similar separations. The dynamical unfolding scenario is disfavored because it predicts highly eccentric wide tertiaries, which is inconsistent with our findings. For the Kozai-Lidov mechanism to be effective for wide tertiaries at $>10^3$ AU, the initial separations of the inner binaries need to be $>3$ AU. Future theoretical investigations are needed to explore the parameter space at these large initial separations and large tertiary separations.

Accepted for publication in MNRAS. Key figures are Fig.4 and Fig.7

References in corpus (24)

• The Gaia mission
• Modules for Experiments in Stellar Astrophysics (MESA)
• A million binaries from Gaia eDR3: sample selection and validation of Gaia parallax uncertainties
• Tertiary companions to close spectroscopic binaries
• Gaia Early Data Release 3 -- Catalogue validation
• Contact Binaries with Additional Components.I. The Extant Data
• Mergers and Obliquities in Stellar Triples
• A time-resolved picture of our Milky Way's early formation history
• Friends of Hot Jupiters. IV. Stellar companions beyond 50 AU might facilitate giant planet formation, but most are unlikely to cause Kozai-Lidov migration
• Astrometric Identification of Nearby Binary Stars I: Predicted Astrometric Signals
• A catalog of wide binary and multiple systems of bright stars from Gaia-DR2 and the Virtual Observatory
• TIC 168789840: A Sextuply-Eclipsing Sextuple Star System
• Stellar Companions to TESS Objects of Interest: A Test of Planet-Companion Alignment
• A Possible Alignment Between the Orbits of Planetary Systems and their Visual Binary Companions
• 97 Eclipsing Quadruple Star Candidates Discovered in TESS Full Frame Images
• Wide twin binaries are extremely eccentric: evidence of twin binary formation in circumbinary disks
• Discovery of a double eclipsing binary with periods near a 3:2 ratio
• Variability, periodicity and contact binaries in WISE
• Very wide companion fraction from Gaia DR2: a weak or no enhancement for hot jupiter hosts, and a strong enhancement for contact binaries
• Binary parameters from astrometric and spectroscopic errors--candidate hierarchical triples and massive dark companions in Gaia DR3
• Resolved Gaia Triples
• On the phase-mixed eccentricity and inclination distributions of wide binaries in the Galaxy
• Enhancement of Double-Close-Binary Quadruples
• Wide binaries from the H3 survey: the thick disk and halo have similar wide binary fractions

Cited by in corpus (8)

• Mass-ratio distribution of contact binary stars
• Wide binary stars formed in the turbulent interstellar medium
• Spectroscopic Orbits of Subsystems in Multiple Stars. X (Summary)
• Exploring Thousands of Nearby Hierarchical Systems with Gaia and Speckle Interferometry
• Binary imposters: Mergers in massive hierarchical triple stars
• The Evolution of Binaries Embedded Within Common Envelopes
• Dynamical masses across the Hertzsprung-Russell diagram
• Massive stellar triples on the edge: A numerical study of the evolution and final outcomes of destabilized massive triples