Tidal Dissipation in Stars and Giant Planets

Ogilvie, Gordon I.

doi:10.1146/annurev-astro-081913-035941

Cited by 385 publications

(380 citation statements)

References 165 publications

(180 reference statements)

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“…There is no obvious relation between the gyrochronological age estimates for these stars and the estimated time scale for tidal interactions between the star and the planet. This may not be surprising given that τ tidal is uncertain by a few orders of magnitude (Ogilvie 2014). It is also apparent that there is an even spread of τ gyro values from very young ages up to a maximum value of a few Gyr, i.e.…”

Section: Discussionmentioning

confidence: 99%

“…Also given in Table 4 is τ tidal , which is a very approximate estimate of the time scale for tidal interactions between the star and the planet (Albrecht et al 2012). It must be emphasised that the actual time scale for tidal spin-up in these systems is uncertain by a few orders of magnitude (Ogilvie 2014). For multi-planet systems, τ tidal applies to the innermost planet.…”

Section: Gyrochronological Age Estimatesmentioning

confidence: 99%

“…For the other stars the agreement between the two age estimates is partly due to the large uncertainty in one or both of these age estimates. The time scale for tidal spin-up of the star depends sensitively on the structure of the star and whether there is any resonance between the orbit of the planet and internal gravity wave modes in the star (Ogilvie 2014), so we should not expect that there is a precise value of log(τ tidal /yr) that divides systems with and without tidal spin-up. Nevertheless, the good agreeement between the isochronal and gyrochronological age estimates for HD 209458 and CoRoT-4 suggests that tidal spin-up for planet host stars may be inefficient for systems with log(τ tidal /yr) > ∼ 12.5.…”

Section: Qatar-2 and Inflated K-dwarfsmentioning

confidence: 99%

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Comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars

Maxted

Serenelli

Southworth

2015

A&A

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Context. Tidal interactions between planets and their host stars are not well understood, but may be an important factor in their formation, structure, and evolution. Previous studies suggest that these tidal interactions may be responsible for discrepancies between the ages of exoplanet host stars estimated using stellar models (isochronal age estimates) and age estimates based on the stars' rotation periods (gyrochronological age estimates). Recent improvements in our understanding of the rotational evolution of single stars and a substantial increase in the number of exoplanet host stars with accurate rotation period measurements make it worthwhile to revisit this question. Aims. Our aim is to determine whether the gyrochronological age estimates for transiting exoplanet host stars with accurate rotation period measurements are consistent with their isochronal age estimates, and whether this is indicative of tidal interaction between the planets and their host stars. Methods. We have compiled a sample of 28 transiting exoplanet host stars with measured rotation periods, including two stars (HAT-P-21 and WASP-5) for which the rotation period based on the light curve modulation is reported here for the first time. We use our recently developed Bayesian Markov chain Monte Carlo method to determine the joint posterior distribution for the mass and age of each star in the sample. We extend our Bayesian method to include a calculation of the posterior distribution of the gyrochronological age estimate that accounts for the uncertainties in the mass and age, the strong correlation between these values, and the uncertainties in the mass-rotation-age calibration. Results. The gyrochronological age estimate (τ gyro ) is significantly lower than the isochronal age estimate for about half of the stars in our sample. Tidal interactions between the star and planet are a reasonable explanation for this discrepancy in some cases, but not all. The distribution of τ gyro values is evenly spread from very young ages up to a maximum value of a few Gyr, i.e. there is no obvious pileup of stars at very low or very high values of τ gyro as might be expected if some evolutionary or selection effect were biasing the age distribution of the stars in this sample. There is no clear correlation between τ gyro and the strength of the tidal force on the star due to the innermost planet. There is clear evidence that the isochronal age estimates for some K-type stars are too high, and this may also be the case for some G-type stars. This may be the result of magnetic inhibition of convection. The densities of HAT-P-11 and WASP-84 are too high to be reproduced by any stellar models within the observed constraints on effective temperature and metallicity. These stars may have strongly enhanced helium abundances. There is currently no satisfactory explanation for the discrepancy between the young age for CoRoT-2 estimated from either gyrochronology or its high lithium abundance, and the extremely old age for its K-type stellar companion...

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Section: Discussionmentioning

confidence: 99%

Section: Gyrochronological Age Estimatesmentioning

confidence: 99%

Section: Qatar-2 and Inflated K-dwarfsmentioning

confidence: 99%

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Comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars

Maxted

Serenelli

Southworth

2015

A&A

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“…Ogilvie 2014). Tidal dissipation inside hot Jupiters (with orbital periods shorter than 10 days) is thought to play an important role in their formation (e.g.…”

Section: Introductionmentioning

confidence: 99%

Non-linear tides in a homogeneous rotating planet or star: global modes and elliptical instability

Barker

Braviner

Ogilvie

2016

Mon. Not. R. Astron. Soc.

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We revisit the global modes and instabilities of homogeneous rotating ellipsoidal fluid masses, which are the simplest global models of rotationally and tidally deformed gaseous planets or stars. The tidal flow in a short-period planet may be unstable to the elliptical instability, a hydrodynamic instability that can drive tidal evolution. We perform a global (and local WKB) analysis to study this instability using the elegant formalism of Lebovitz & Lifschitz. We survey the parameter space of global instabilities with harmonic orders 5, for planets with spins that are purely aligned (prograde) or anti-aligned (retrograde) with their orbits. In general, the instability has a much larger growth rate if the planetary spin and orbit are anti-aligned rather than aligned. We have identified a violent instability for anti-aligned spins outside of the usual frequency range for the elliptical instability (when n Ω −1, where n and Ω are the orbital and spin angular frequencies, respectively) if the tidal amplitude is sufficiently large. We also explore the instability in a rigid ellipsoidal container, which is found to be quantitatively similar to that with a realistic free surface. Finally, we study the effect of rotation and tidal deformation on mode frequencies. We find that larger rotation rates and larger tidal deformations both decrease the frequencies of the prograde sectoral surface gravity modes. This increases the prospect of their tidal excitation, potentially enhancing the tidal response over expectations from linear theory. In a companion paper, we use our results to interpret global simulations of the elliptical instability.

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“…Adopting a constant Q implies that the time lag between the maximum of the tidal potential and the tidal bulge in each body scales with the orbital period and that the relevant tidal frequency is the orbital frequency. This may not give identical numerical factors as other formulations of tidal friction but, given our lack of knowledge of the actual values of Q and its dependence on tidal frequency, this approximation remains reasonable (see Mathis & Remus 2013;Ogilvie 2014 for detailed reviews on tidal dissipation). We use a Skumanich-type law for magnetic braking with a torque of magnitude Γ mb = −α mb C Ω 3 , where the value of α mb is estimated from observed rotation periods of stars of different ages.…”

Section: Interplay Between the Tidal Torque And The Wind Torquementioning

confidence: 99%

Can brown dwarfs survive on close orbits around convective stars?

Damiani

Díaz

2016

A&A

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Context. The mass range of brown dwarfs extends across the planetary domain to stellar objects. There is a relative paucity of brown dwarfs companions around FGKM-type stars compared to exoplanets for orbital periods of less than a few years, but most of the short-period brown dwarf companions that are fully characterised by transits and radial velocities are found around F-type stars. Aims. We examine the hypothesis that brown dwarf companions could not survive on close orbit around stars with important convective envelopes because the tides and angular momentum loss, the result of magnetic braking, would lead to a rapid orbital decay with the companion being quickly engulfed. Methods. We use a classical Skumanich-type braking law and constant time-lag tidal theory to assess the characteristic timescale for orbital decay for the brown dwarf mass range as a function of the host properties. Results. We find that F-type stars may host massive companions for a significantly longer time than G-type stars for a given orbital period, which may explain the paucity of G-type hosts for brown dwarfs with an orbital period less than five days. On the other hand, we show that the small radius of early M-type stars contributes to orbital decay timescales that are only half those of F-type stars, despite their more efficient tidal dissipation and magnetic braking. For fully convective later type M-dwarfs, orbital decay timescales could be orders of magnitude greater than for F-type stars. Moreover, we find that, for a wide range of values of tidal dissipation efficiency and magnetic braking, it is safe to assume that orbital decay for massive companions can be neglected for orbital periods greater than ten days. Conclusions. For orbital periods greater than ten days, brown dwarf occurrence should largely be unaffected by tidal decay, whatever the mass of the host. On closer orbital periods, the rapid engulfment of massive companions could explain the lack of G and K-type hosts in the sample of known systems with transiting brown dwarfs. However, the paucity of M-type hosts cannot be an effect of tidal decay alone, but may be the result of a selection effect in the sample and/or the formation mechanism.

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Tidal Dissipation in Stars and Giant Planets

Cited by 385 publications

References 165 publications

Comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars

Comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars

Non-linear tides in a homogeneous rotating planet or star: global modes and elliptical instability

Can brown dwarfs survive on close orbits around convective stars?

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