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Abstract The Gaia mission has detected many white dwarfs (WDs) in binary and triple configurations, and while observations suggest that triple-stellar systems are common in our Galaxy, not much attention was devoted to WDs in triples. For stability reasons, these triples must have hierarchical configurations, i.e., two stars are on a tight orbit (the inner binary), with the third companion on a wider orbit about the inner binary. In such a system, the two orbits torque each other via the eccentric Kozai–Lidov mechanism, which can alter the orbital configuration of the inner binary. We simulate thousands of triple-stellar systems for over 10 Gyr, tracking gravitational interactions, tides, general relativity, and stellar evolution up to their WD fate. As demonstrated here, three-body dynamics coupled with stellar evolution is a critical channel to form tight WD binaries or merge a WD binary. Among these triples, we explore their manifestations as cataclysmic variables, Type Ia supernovae, and gravitational-wave events. The simulated systems are then compared to a sample of WD triples selected from the Gaia catalog. We find that including the effect of mass-loss-induced kicks is crucial for producing a distribution of the inner binary–tertiary separations that is consistent with Gaia observations. Lastly, we leverage this consistency to estimate that, at minimum, 30% of solar-type stars in the local 200 pc were born in triples.
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Cataclysmic Variables in Triples: Formation Models and New Discoveries
Abstract The formation of cataclysmic variables (CVs) has long been modeled as a product of common envelope evolution (CEE) in isolated binaries. However, a significant fraction of intermediate-mass stars—the progenitors of the white dwarfs (WDs) in CVs—are in triples. We therefore investigate the importance of triple star dynamics in CV formation. Using Gaia astrometry and existing CV catalogs, we construct a sample of ∼50 CVs in hierarchical triples within 1 kpc of the Sun, containing main-sequence and WD tertiaries at separations of 100–30,000 au. We infer that at least 10% of CVs host wide tertiaries. To interpret this discovery, we evolve a population of 2000 triples using detailed three-body simulations, 47 of which become CVs. We predict that 20% of CVs in triples form without ever experiencing CEE, where the WD and donor are brought together by the eccentric Kozai-Lidov mechanism after the formation of the WD. These systems favor larger donor stars and longer birth orbital periods (8–20 hr) than typical CVs. Among systems that do undergo CEE, about half would not have interacted without the presence of the tertiary. Triple formation channels both with and without CEE require initially wide inner orbits (≳1 au), which in turn require larger tertiary separations to be stable. Consistent with this prediction, we find that the observed Gaia CV triples have wider separations on average than normal wide binaries selected in the same way. Our work underscores the importance of triples in shaping interacting binary populations including CVs, ultracompact binaries, and low-mass X-ray binaries.
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- Award ID(s):
- 2206428
- PAR ID:
- 10647810
- Publisher / Repository:
- Publications of the Astronomical Society of the Pacific
- Date Published:
- Journal Name:
- Publications of the Astronomical Society of the Pacific
- Volume:
- 137
- Issue:
- 7
- ISSN:
- 0004-6280
- Page Range / eLocation ID:
- 074201
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1088/1538-3873/add5a1
