Julien de Wit, Michaël Gillon, Brice-Olivier Demory, Sara Seager
Context. Mapping the brightness distribution of exoplanets is the next
frontier for exoplanet infrared photometry studies. For tidally-locked hot
Jupiters that transit and are eclipsed by their host star with non-zero impact
parameter, the first steps are now possible.
Aims. The aim is to use eclipse scanning from occultation ingress/egress and
phase curve measurements to constrain exoplanet large-scale brightness
structure.
Methods. We use archived Spitzer/IRAC 8 {\mu}m data of HD189733 in a global
MCMC procedure encompassing six transits, eight secondary eclipses, and a phase
curve in a two-step analysis. The first step derives the planet-star system
parameters. The second step investigates the structure found in eclipse
scanning, using the previous planet-star system parameter derivation as
Gaussian priors.
Results. We find a 5-sigma deviation from the expected occultation
ingress/egress shape for a uniform brightness disk, and demonstrate that this
is dominated by large-scale brightness structure and not an occultation timing
offset due to a non-zero eccentricity. Our analysis yields a 2D brightness
temperature distribution showing a large-scale asymmetric hot spot whose finer
structure is limited by the data quality and planet orbit geometry. We also
present an improved upper limit for eccentricity, e<0.0081 (95% confidence).
Conclusions. Reanalysis of archived HD 189733 data revealed brightness
structure by using global analysis that mitigated systematics. Future eclipse
scanning observations of the same exoplanet at other wavelengths will probe
different atmosphere layers, ultimately generating a large-scale 3D map.
View original:
http://arxiv.org/abs/1202.3829
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