Tidal dissipation in planet-hosting stars: damping of spin-orbit misalignment and survival of hot Jupiters

By D. Lai. 2011

135 citations recorded by the source corpus.

Observations of hot Jupiters around solar-type stars with very short orbital periods (∼1 d) suggest that tidal dissipation in such stars is not too efficient so that these planets can survive against rapid orbital decay. This is consistent with recent theoretical works, which indicate that the tidal quality factor, Q★, of planet-hosting stars can indeed be much larger than the values inferred from the circularization of stellar binaries. On the other hand, recent measurements of Rossiter–McLaughlin effects in transiting hot Jupiter systems not only reveal that many such systems have misaligned stellar spin with respect to the orbital angular momentum axis, but also show that systems with cooler host stars tend to have aligned spin and orbital axes. Winn et al. suggested that this obliquity–temperature correlation may be explained by efficient damping of stellar obliquity due to tidal dissipation in the convection zone of the star. This explanation, however, is in apparent contradiction with the survival of these short-period hot Jupiters. We show that in the solar-type parent stars of close-in exoplanetary systems, the effective tidal Q★ governing the damping of stellar obliquity can be much smaller than that governing orbital decay. This is because, for misaligned systems, the tidal potential contains a Fourier component with frequency equal to the stellar spin frequency (in the rotating frame of the star) and rotating opposite to the stellar spin. This component can excite inertial waves in the convective envelope of the star, and the dissipation of inertial waves then leads to a spin–orbit alignment torque and a spin-down torque, but not orbital decay. By contrast, for aligned systems, such inertial wave excitation is forbidden since the tidal forcing frequency is much larger than the stellar spin frequency. We derive a general effective tidal evolution theory for misaligned binaries, taking account of different tidal responses and dissipation rates for different tidal forcing components.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/d0c10a3f8bf09e59d1a939ce7aafd3f803473f40

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Citations in the corpus

The GAPS Programme with HARPS-N at TNG - XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets (2017, unknown): “Tidal dissipation inside the planet mainly acts to circularise and shrink the planetary orbit, while tides inside the star act to realign the orbital plane with the stellar equator (Lai 2012).”
WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star (2015, background): “Both solutions are in excellent agreement and place the planet in a nearly polar orbit around its star, which is clearly a remarkable configuration as noted by e.g. Lai 2012 and Rogers & Lin 2013.”
FRIENDS OF HOT JUPITERS. I. A RADIAL VELOCITY SEARCH FOR MASSIVE, LONG-PERIOD COMPANIONS TO CLOSE-IN GAS GIANT PLANETS (2013, background): “However, the exact nature of this tidal realignment is still debated (Lai 2012; 22 Rogers & Lin 2013; Valsecchi & Rasio 2014).”
OBLIQUITIES OF HOT JUPITER HOST STARS: EVIDENCE FOR TIDAL INTERACTIONS AND PRIMORDIAL MISALIGNMENTS (2012, background): “Because of the obliquity near 90◦ tides couple only weakly to the stellar rotation (Lai 2012).”
The Occurrence and Architecture of Exoplanetary Systems (2014, background): “Lai (2012) provided one possible solution, by giving an example of a more complex tidal theory in which realignment can be much faster than orbital decay.”
Tidal Dissipation in Stars and Giant Planets (2014, background): “Detailed dynamical analyses of this system identify these oscillations as tidally excited g modes in the two stars and reveal evidence for three-mode coupling (Fuller & Lai 2012a; Burkart et al. 2012; O’Leary & Burkart 2014).”
INTERNAL GRAVITY WAVES IN MASSIVE STARS: ANGULAR MOMENTUM TRANSPORT (2013, background): “On the other hand, if one relies on the dynamical tide introduced by Lai (2012) then planets evolve to aligned or anti-aligned systems, contrary to observations.”