The Consequences of the Photoeccentric Effect on Proto Hot Jupiters

THE PHOTOECCENTRIC EFFECT AND PROTO-HOT JUPITERS. III. A PAUCITY OF PROTO-HOT JUPITERS ON SUPER-ECCENTRIC ORBITS

Authors:

Dawson et al

Abstract:

Gas giant planets orbiting within 0.1 AU of their host stars are unlikely to have formed in situ and are evidence for planetary migration. It is debated whether the typical hot Jupiter smoothly migrated inward from its formation location through the proto-planetary disk, or was perturbed by another body onto a highly eccentric orbit, which tidal dissipation subsequently shrank and circularized during close stellar passages. Socrates and collaborators predicted that the latter model should produce a population of super-eccentric proto-hot Jupiters readily observable by Kepler. We find a paucity of such planets in the Kepler sample, which is inconsistent with the theoretical prediction with 96.9% confidence. Observational effects are unlikely to explain this discrepancy. We find that the fraction of hot Jupiters with an orbital period P greater than 3 days produced by the star-planet Kozai mechanism does not exceed (at two-sigma) 44%. Our results may indicate that disk migration is the dominant channel for producing hot Jupiters with P greater than 3 days. Alternatively, the typical hot Jupiter may have been perturbed to a high eccentricity by interactions with a planetary rather than stellar companion, and began tidal circularization much interior to 1 AU after multiple scatterings. A final alternative is that early in the tidal circularization process at high eccentricities tidal circularization occurs much more rapidly than later in the process at low eccentricities, although this is contrary to current tidal theories.

What is the Photoeccentric Effect?

How Low Can You Go? The Photoeccentric Effect for Planets of Various Sizes

Authors:

Price et al

Abstract:

It is well-known that the light curve of a transiting planet contains information about the planet's orbital period and size relative to the host star. More recently, it has been demonstrated that a tight constraint on an individual planet's eccentricity can sometimes be derived from the light curve via the "photoeccentric effect," the effect of a planet's eccentricity on the shape and duration of its light curve. This has only been studied for large planets and high signal-to-noise scenarios, raising the question of how well it can be measured for smaller planets or low signal-to-noise cases. We explore the limits of the photoeccentric effect over a wide range of planet parameters. The method hinges upon measuring g directly from the light curve, where g is the ratio of the planet's speed (projected on the plane of the sky) during transit to the speed expected for a circular orbit. We find that when the signal-to-noise in the measurement of g is less than 10, the ability to measure eccentricity with the photoeccentric effect decreases. We develop a "rule of thumb" that for per-point relative photometric uncertainties σ={10−3,10−4,10−5}, the critical values of planet-star radius ratio are Rp/R⋆≈{0.1,0.05,0.03} for Kepler-like 30-minute integration times. We demonstrate how to predict the best-case uncertainty in eccentricity that can be found with the photoeccentric effect for any light curve. This clears the path to study eccentricities of individual planets of various sizes in the Kepler sample and future transit surveys.