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Eccentricity and spin-orbit misalignment in short-period stellar binaries as a signpost of hidden tertiary companions

Anderson, Kassandra R. and Lai, Dong and Storch, Natalia I. (2017) Eccentricity and spin-orbit misalignment in short-period stellar binaries as a signpost of hidden tertiary companions. Monthly Notices of the Royal Astronomical Society, 467 (3). pp. 3066-3082. ISSN 0035-8711. doi:10.1093/mnras/stx293.

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Eclipsing binaries are observed to have a range of eccentricities and spin-orbit misalignments (stellar obliquities). Whether such properties are primordial or arise from post-formation dynamical interactions remains uncertain. This paper considers the scenario in which the binary is the inner component of a hierarchical triple stellar system, and derives the requirements that the tertiary companion must satisfy in order to raise the eccentricity and obliquity of the inner binary. Through numerical integrations of the secular octupole-order equations of motion of stellar triples, coupled with the spin precession of the oblate primary star due to the torque from the secondary, we obtain a simple, robust condition for producing spin-orbit misalignment in the inner binary. In order to excite appreciable obliquity, the precession rate of the stellar spin axis must be smaller than the orbital precession rate due to the tertiary companion. This yields quantitative requirements on the mass and orbit of the tertiary. We also present new analytic expressions for the maximum eccentricity and range of inclinations allowing eccentricity excitation (Lidov–Kozai window), for stellar triples with arbitrary masses and including the non-Keplerian potentials introduced by general relativity, stellar tides and rotational bulges. The results of this paper can be used to place constraints on unobserved tertiary companions in binaries that exhibit high eccentricity and/or spin-orbit misalignment, and will be helpful in guiding efforts to detect external companions around stellar binaries. As an application, we consider the eclipsing binary DI Herculis, and identify the requirements that a tertiary companion must satisfy to produce the observed spin-orbit misalignment.

Item Type:Article
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URLURL TypeDescription Paper
Lai, Dong0000-0002-1934-6250
Additional Information:© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 January 31. Received 2017 January 28; in original form 2016 October 8. Published: 02 February 2017. We thank the referee, Alexandre Correia, for useful comments. This work has been supported in part by NASA grants NNX14AG94G and NNX14AP31G, and a Simons Fellowship from the Simons Foundation. KRA is supported by the NSF Graduate Research Fellowship Program under Grant No. DGE-1144153. NIS is supported by a Sherman Fairchild Fellowship at Caltech.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Simons FoundationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1144153
Sherman Fairchild FoundationUNSPECIFIED
Subject Keywords:binaries: close, binaries: eclipsing, stars: kinematics and dynamics
Issue or Number:3
Record Number:CaltechAUTHORS:20170428-144222546
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Official Citation:Kassandra R. Anderson, Dong Lai, Natalia I. Storch; Eccentricity and spin-orbit misalignment in short-period stellar binaries as a signpost of hidden tertiary companions. Mon Not R Astron Soc 2017; 467 (3): 3066-3082. doi: 10.1093/mnras/stx293
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77066
Deposited By: Tony Diaz
Deposited On:28 Apr 2017 23:52
Last Modified:15 Nov 2021 17:27

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