May 9th, 2014: Hot and shiny: Atmospheric characterization of the hot Jupiter exoplanet Kepler-13Ab

One of the expanding fields of exoplanet research is the detailed characterization of exoplanets, including the properties of their atmospheres. This is currently being done for a growing sample of the so-called hot Jupiters – gas-giant planets orbiting close-in to their host star – a class of planets with no Solar System analog. I will present the results of our atmospheric study of the unique transiting exoplanet Kepler-13Ab. It is one of only two known short-period (1.76 day) transiting planets orbiting a bright hot A-type star (Teff = 7,650 K), and the host star is part of a hierarchical triple system. We have studied the planet’s emission spectrum by observing the planet’s occultation (secondary eclipse; when the planet moves behind the host star) using data from the optical to the IR, obtained with the Kepler and Spitzer space telescopes along with a ground-based observation in the near-IR. We derive a temperature of 2,750 K of the planet’s day-side hemisphere, as hot as the smallest main-sequence stars. We find evidence for a high geometric albedo (~0.3), a few times larger than that of most other hot Jupiters, and for the presence of atmospheric inversion. In addition, our revised planetary radius (1.4 Jupiter radius) is significantly smaller than previously thought, and our revised planetary mass, from measuring the beaming effect and ellipsoidal distortion in the Kepler orbital phase curve, is 5 – 8 Jupiter mass. Therefore, Kepler-13Ab is a massive high-density hot Jupiter. Time allowing, I will show how the difference between the Kepler occultation time and transit (primary eclipse) time is half a minute shorter than expected from the light travel time delay across the orbit, and discuss possible causes.

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