Atmospheric characterization of the hot Jupiter exoplanet Kepler-13Ab

One of the expanding fields of exoplanet study 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 that does not exist in the Solar

System. 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) planets orbiting a bright (V = 9.95 mag), hot

A-type star (Teff = 7,650 K). We have observed the planetג€™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. For the planetary hemisphere facing the star we derive a

temperature of 2,750 K, comparable to the smallest main-sequence

stars. We find evidence for a high geometric albedo, of about 0.3,

which is unusually high for gas-giant planets, and identify the

presence of atmospheric inversion, where the temperature increases

with decreasing pressure. 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 phase curve, is 5 - 8 Jupiter

mass. Therefore, this planet is a massive high-density hot Jupiter,

with radius similar to those of other hot Jupiters. Finally, we find

that the difference between the Kepler occultation time and transit

time is half a minute shorter than expected from the light travel time

delay, and discuss possible causes.