Spin-Orbit Evolution of Short-Period Planets

By I. Dobbs-Dixon, D.N.C. Lin, Rosemary A. Mardling. 2004

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The negligible eccentricity of all extrasolar planets with periods less than 6 days can be accounted for by dissipation of tidal disturbances within their envelopes that are induced by their host stars. In the period range of 7-21 days, planets with circular orbits coexist with planets with eccentric orbits. These are referred to as the borderline planets. We propose that this discrepancy can be attributed to the variation in spin-down rates of young stars. In particular, prior to spin-down, dissipation of a planet's tidal disturbance within the envelope of a sufficiently rapidly spinning star can excite eccentricity growth and, for a more slowly spinning star, at least reduce the eccentricity-damping rate. In contrast, tidal dissipation within the envelope of a slowly spinning low-mass mature star can enhance the eccentricity-damping process. On the basis of these results, we suggest that short-period planets around relatively young stars may have a much larger dispersion in eccentricity than those around mature stars. We also suggest that because the rate of angular momentum loss from G and K dwarfs via stellar winds is much faster than the tidal transfer of angular momentum between themselves and their very short (3-4 days) period planets, they cannot establish a dynamical configuration in which the stellar and planetary spins are approximately parallel and synchronous with the orbital frequency. In principle, however, such configurations may be established for planets (around G and K dwarfs) with orbital periods of up to several weeks. In contrast to G and K dwarfs, the angular momentum loss due to stellar winds is much weaker in F dwarfs. It is therefore possible for synchronized short-period planets to exist around such stars. The planet around Tau Boo is one such example.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/57088d10fc3599d0442e6064016055ca611ba802

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Citations in the corpus

• The Transit Light Curve Project. I. Four Consecutive Transits of the Exoplanet XO-1b (2006, background): “…for a non-zero eccentricity, and in the absence of any evidence for additional bodies in the system, it is expected that tidal interactions have had sufficient time to circularize the orbit (see, e.g., Rasio et al. 1996; Trilling 2000; Dobbs-Dixon et al. 2004). on the planet-to-star area ratio.”
• Predicting low-frequency radio fluxes of known extrasolar planets (2007, background): “For the small orbital distances relevant for Hot Jupiters, the planetary orbits are circular because of tidal dissipation (Goldreich & Soter, 1966; Dobbs-Dixon et al., 2004; Halbwachs et al., 2005).”
• On the tidal evolution of Hot Jupiters on inclined orbits (2009, methodology): “For an F-dwarf (like τ Boo), it has been proposed that only the outer convective envelope (of mass fraction ∼ ?) participates in angular momentum exchange with the orbit (Marcy et al. 1997; Dobbs-Dixon et al. 2004; Donati et al. 2008).”
• OBSERVATIONAL EVIDENCE FOR TIDAL DESTRUCTION OF EXOPLANETS (2009, background): “…have generally ignored the effect of the tide raised on the host star, which plays a significant role in the evolution of the orbits of close-in exoplanets (Trilling et al. 1998; Dobbs-Dixon et al. 2004; Adams & Laughlin 2006; Jackson et al. 2008a; Levrard et al. 2009; Barker & Ogilvie 2009).”
• Transiting exoplanets from the CoRoT space mission . VI. CoRoT-Exo-3b: the first secure inhabitant of the brown-dwarf desert (2008, background): “Given the relatively large mass and short period of the companion, one might expect it to have synchronized the rotation of its host star to its orbital period via tidal interaction (Dobbs-Dixon et al. 2004; Jackson et al. 2008).”
• WASP-19b: THE SHORTEST PERIOD TRANSITING EXOPLANET YET DISCOVERED (2010, background): “By integrating the coupled equations of orbital eccentricity and separation (Dobbs-Dixon et al. 2004) while conserving the total angular momentum of the system, we can model the future evolution of the planet as it spirals inward and further spins up the host star.”
• Is tidal heating sufficient to explain bloated exoplanets? Consistent calculations accounting for finite initial eccentricity (2010, methodology): “(19) to rewrite the tidal equation and to keepQ′ constant instead of ∆t as done by, for example, Mardling & Lin (2002), Dobbs-Dixon et al. (2004) and Barker & Ogilvie (2009), one must keep in mind that this procedure is not equivalent either to the constant phase lag (i.e. constant Q) or time lag…”
• Tidal dissipation in planet-hosting stars: damping of spin-orbit misalignment and survival of hot Jupiters (2011, background): “Many previous works on tidal evolution in hot Jupiter systems (e.g., Rasio et al. 1996; Sasselov 2003; Dobbs-Dixon et al. 2004; Barker & Ogilvie 2009; Jackson et al. 2009; Levrard et al. 2009; Hansen 2010; Matsumura et al. 2010) were based on the weak friction theory of equilibrium tides.”
• The Transit Light Curve Project. V. System Parameters and Stellar Rotation Period of HD 189733 (2006, background): “For most of the analysis we assumed that the orbital eccentricity e is zero, because the expected timescale of tidal circularization is short in the absence of excitations from other planets (see, e.g., Rasio et al. 1996; Trilling 2000; Dobbs-Dixon et al. 2004; Adams&Laughlin 2006).”
• EXOPLANETARY SPIN–ORBIT ALIGNMENT: RESULTS FROM THE ENSEMBLE OF ROSSITER–MCLAUGHLIN OBSERVATIONS (2009, background): “For example, if a hot Jupiter migrated inward before its host star contracted onto the main sequence, the distended stellar envelope could produce more pronounced tidal effects (Zahn & Bouchet 1989; Dobbs-Dixon et al. 2004).”
• Tidal Heating of Extrasolar Planets (2008, background): “Understanding of the frequency dependence of Q 0pwill allow the formulation of governing equations that havemore credibility for large values of e (e.g.,Mardling &Lin 2002) or for cases with a comparable rotation period of the star and orbital period of the planet (Dobbs-Dixon et al. 2004).”
• TIDAL EVOLUTION OF CLOSE-IN PLANETS (2010, background): “In other words, the eccentricity damps on the timescale determined by tidal dissipation in the planet, as previously shown by many authors (e.g., Rasio et al. 1996; Dobbs-Dixon et al. 2004; Mardling & Lin 2004).”
• Tidal obliquity evolution of potentially habitable planets (2011, background): “Various other studies only include the impact of eccentricity on tidal locking, neglecting thecontribution from obliquity (Goldreich & Soter 1966; Goldreich 1966; Eggleton et al. 1998; Trilling 2000; Showman & Guillot 2002; Dobbs-Dixon et al. 2004; Selsis et al. 2007; Barnes et al. 2008).”