The 8 Micron Phase Variation of the Hot Saturn HD 149026b

Understand

We monitor the star HD 149026 and its Saturn-mass planet at 8.0 micron over slightly more than half an orbit using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope.

• We find an increase of 0.0227% +/- 0.0066% (3.4 sigma significance) in the combined planet-star flux during this interval.
• The minimum flux from the planet is 45% +/- 19% of the maximum planet flux, corresponding to a difference in brightness temperature of 480 +/- 140 K between the two hemispheres.
• We derive a new secondary eclipse depth of 0.0411% +/- 0.0076% in this band, corresponding to a dayside brightness temperature of 1440 +/- 150 K.