Eccentricities and Stellar Obliquities in Hot and Warm Jupiter Systems with External Perturbers

Kassandra Anderson (Cornell) - September 17, 2018 at 12:10 pm

Hot Jupiters (HJs) and warm Jupiters (WJs) exhibit several observational puzzles, including stellar spin-orbit misalignments (obliquities) in many HJ systems, and substantial eccentricities in many WJ systems. This talk considers the role of an external planetary companion in generating such eccentricities and stellar obliquities. In Part I of the talk, we investigate whether an external companion may induce secular eccentricity oscillations in WJ systems, through an apsidal precession resonance (when the companion is eccentric and co-planar), or Lidov-Kozai oscillations (when the companion is sufficiently inclined). We consider the sample of WJs with detected outer companions, and for each system, identify the range of mutual inclinations needed to generate the observed WJ eccentricity. For most systems, we find that high inclinations are needed so that Lidov-Kozai cycles are induced; the outer companions are typically not eccentric enough to generate the observed WJ eccentricity in a low-inclination configuration. Observational constraints on mutual inclinations in two-planet systems are needed to clarify the role of external companions in secularly exciting WJ eccentricities. In Part II of the talk, we consider the possibility of an inclined companion in exciting the stellar obliquity due to a secular resonance, occurring when the precession rate of the stellar spin axis (driven by the inner planet) becomes comparable to the nodal precession rate of the inner planet (driven by the outer planet). Due to their close proximity to the host star, HJs have strongly-coupled stellar spin and orbital axes, and a strong perturber is required to raise the obliquity, located within 1-2 AU. In contrast, WJ systems experience weaker spin-orbit coupling, and obliquity excitation may be achieved for more distant perturbers, located at tens of AU. Unlike HJs, WJ stellar obliquities have not been extensively probed. We predict WJs may have significant obliquities due to resonant excitation, especially those orbiting cool host stars.

The seminar will be held in 131A Campbell Hall.

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