We report 78 secondary eclipse depths for a sample of 36 transiting hot
Jupiters observed at 3.6- and 4.5 microns using the Spitzer Space Telescope.
Our eclipse results for 27 of these planets are new, and include highly
irradiated worlds such as KELT-7b, WASP-87b, WASP-76b, and WASP-64b, and
important targets for JWST such as WASP-62b. We find that WASP-62b has a
slightly eccentric orbit e cos(omega) = 0.00614+/- 0.00064, and we confirm the
eccentricity of HAT-P-13b and WASP-14b. The remainder are individually
consistent with circular orbits, but we find statistical evidence for
eccentricity increasing with orbital period in our range from 1 to 5 days. Our
day-side brightness temperatures for the planets yield information on albedo
and heat redistribution, following Cowan and Agol (2011). Planets having
maximum day side temperatures exceeding ~ 2200K are consistent with zero albedo
and distribution of stellar irradiance uniformly over the day-side hemisphere.
Our most intriguing result is that we detect a systematic difference between
the emergent spectra of these hot Jupiters as compared to blackbodies. The
ratio of observed brightness temperatures, Tb(4.5)/Tb(3.6), increases with
equilibrium temperature by 100 +/- 24 parts-per-million per Kelvin, over the
entire temperature range in our sample (800K to 2500K). No existing model
predicts this trend over such a large range of temperature. We suggest that
this may be due to a structural difference in the atmospheric temperature
profile between the real planetary atmospheres as compared to models