We present secondary eclipse observations of the highly irradiated transiting brown dwarf KELT-1b .
These observations represent the first constraints on the atmospheric dynamics of a highly irradiated brown dwarf , the atmospheres of irradiated giant planets at high surface gravity , and the atmospheres of brown dwarfs that are dominated by external , rather than internal , energy .
Using the Spitzer Space Telescope , we measure secondary eclipse depths of 0.195 \pm 0.010 % at 3.6 \mu m and 0.200 \pm 0.012 % at 4.5 \mu m. We also find tentative evidence for the secondary eclipse in the z ^ { \prime } band with a depth of 0.049 \pm 0.023 % .
These measured eclipse depths are most consistent with an atmosphere model in which there is a strong substellar hotspot , implying that heat redistribution in the atmosphere of KELT-1b is low .
While models with a more mild hotspot or even with dayside heat redistribution are only marginally disfavored , models with complete heat redistribution are strongly ruled out .
The eclipse depths also prefer an atmosphere with no TiO inversion layer , although a model with TiO inversion is permitted in the dayside heat redistribution case , and we consider the possibility of a day-night TiO cold trap in this object .
For the first time , we compare the IRAC colors of brown dwarfs and hot Jupiters as a function of effective temperature .
Importantly , our measurements reveal that KELT-1b has a [ 3.6 ] - [ 4.5 ] color of 0.07 \pm 0.11 , identical to that of isolated brown dwarfs of similarly high temperature .
In contrast , hot Jupiters generally show redder [ 3.6 ] - [ 4.5 ] colors of \sim 0.4 , with a very large range from \sim 0 to \sim 1 .
Evidently , despite being more similar to hot Jupiters than to isolated brown dwarfs in terms of external forcing of the atmosphere by stellar insolation , KELT-1b appears to have an atmosphere most like that of other brown dwarfs .
This suggests that surface gravity is very important in controlling the atmospheric systems of substellar mass bodies .