Analysis of Spin-Orbit Misalignment in the Eclipsing Binary Di Herculis

Philippov, Alexander; Rafikov, Roman R.

doi:10.1088/0004-637x/768/2/112

Cited by 50 publications

(30 citation statements)

References 27 publications

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“…Figure 13 depicts the combinations of m2 and a out,eff that lead to A < 3 for the primary member (shaded region). Note that we have assumed a primary stellar spin period P = 1.25 days -this rapid rotation rate is consistent with the observed v sin i, and the estimated value by Philippov & Rafikov (2013) using gravity darkening. Inspecting Fig.…”

Section: Application: DI Herculissupporting

confidence: 79%

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

Anderson

Lai

Storch

2017

Monthly Notices of the Royal Astronomical Society

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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.

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Section: Application: DI Herculissupporting

confidence: 79%

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

Anderson

Lai

Storch

2017

Monthly Notices of the Royal Astronomical Society

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“…We also fit a gravity darkening exponent for KOI-368 of y = 0.20 +0.06 −0.04 (β gravity ≈ 0.05). This is significantly lower than simple theoretical model predictions, which is also seen for DI Her (Philippov & Rafikov 2013).…”

Section: Fitting Of System Parametersmentioning

confidence: 58%

A Highly Inclined Orbit for the 110 Day Period M-Dwarf Companion KOI-368.01

Zhou

Huang

2013

ApJ

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We report the detection of asymmetry in the transit light curves of the 110-day period companion to KOI-368, a rapidly rotating A-dwarf. The significant distortion in the transit light curve is attributed to spin-orbit misalignment between the transiting companion and the gravity darkened host star. Our analysis was based on 11 Long Cadence and 2 Short Cadence transits of KOI-368.01 from the Kepler mission, as well as stellar parameters determined from our follow-up spectroscopic observation. We measured the true obliquity between the orbit normal and the stellar rotation axis to be 69 +9 • −10 . We also find a secondary eclipse event with depth 29 ± 3 ppm at phase 0.59, from which the temperature of the companion is constrained to 3060 ± 50 K, indicating that KOI-368.01 is a late M-dwarf. The eccentricity is also calculated from the eclipse to be 0.1429 ± 0.0007. The long period, high obliquity, and low eccentricity of KOI-368.01 allow us to limit a number of proposed theories for the misalignment of binary systems.

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“…Albrecht et al 2009Albrecht et al , 2014. Tentative evidence of axial precession from the variable rotational broadening of stellar spectral lines was presented for DI Herculis as far back as the 1980's (Reisenberger & Guinan 1989), and this has been subsequently supported by recent studies (Albrecht et al 2009;Philippov & Rafikov 2013). Perhaps the clearest evidence of axial precession in stars is in CV Velorum (Albrecht et al 2014).…”

Section: Introductionmentioning

confidence: 86%

On turbulence driven by axial precession and tidal evolution of the spin–orbit angle of close-in giant planets

Barker

2016

Mon. Not. R. Astron. Soc.

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The spin axis of a rotationally deformed planet is forced to precess about its orbital angular momentum vector, due to the tidal gravity of its host star, if these directions are misaligned. This induces internal fluid motions inside the planet that are subject to a hydrodynamic instability. We study the turbulent damping of precessional fluid motions, as a result of this instability, in the simplest local computational model of a giant planet (or star), with and without a weak internal magnetic field. Our aim is to determine the outcome of this instability, and its importance in driving tidal evolution of the spin-orbit angle in precessing planets (and stars). We find that this instability produces turbulent dissipation that is sufficiently strong that it could drive significant tidal evolution of the spin-orbit angle for hot Jupiters with orbital periods shorter than about 10-18 days. If this mechanism acts in isolation, this evolution would be towards alignment or anti-alignment, depending on the initial angle, but the ultimate evolution (if other tidal mechanisms also contribute) is expected to be towards alignment. The turbulent dissipation is proportional to the cube of the precession frequency, so it leads to much slower damping of stellar spin-orbit angles, implying that this instability is unlikely to drive evolution of the spin-orbit angle in stars (either in planetary or close binary systems). We also find that the instability-driven flow can act as a system-scale dynamo, which may play a role in producing magnetic fields in short-period planets.

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Analysis of Spin-Orbit Misalignment in the Eclipsing Binary Di Herculis

Cited by 50 publications

References 27 publications

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

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

A Highly Inclined Orbit for the 110 Day Period M-Dwarf Companion KOI-368.01

On turbulence driven by axial precession and tidal evolution of the spin–orbit angle of close-in giant planets

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