We observed eclipses of the transiting brown dwarf CWW 89Ab at 3.6 \mu m and 4.5 \mu m using Spitzer/IRAC .
The CWW 89 binary system is a member of the 3.0 \pm 0.25 Gyr-old open cluster Ruprecht 147 , and is composed of a Sun-like primary and an early M-dwarf secondary separated by a projected distance of 25 AU .
CWW 89Ab has a radius of 0.937 \pm 0.042 { { R } _ { J } } and a mass of 36.5 \pm 0.1 { { M } _ { J } } , and is on a 5.3 day orbit about CWW 89A with a non-zero eccentricity of e = 0.19 \citep curtis2016 .
We strongly detect the eclipses of CWW 89Ab in both Spitzer channels as \delta _ { 3.6 } = 1147 \pm 213 ppm and \delta _ { 4.5 } = 1097 \pm 225 ppm after correcting for the dilution from CWW 89B .
After accounting for the irradiation that CWW 89Ab receives from its host star , these measurements imply that the brown dwarf has an internal luminosity of \log ( \mathrm { L _ { bol } / \mathrm { L } _ { \odot } } ) = -4.19 \pm 0.14 .
This is 16 times , or 9.3 \sigma , higher than model predictions given the known mass , radius , and age of CWW 89Ab .
As we discuss , this over-luminosity is not explainable by an inaccurate age determination , additional stellar heating , nor tidal heating .
Instead , we suggest that the anomalous luminosity of CWW 89Ab is caused by a dayside temperature inversion – though a significant error in the evolutionary models is also a possibility .
Importantly , a temperature inversion would require a super-stellar C/O ratio in CWW 89Ab ’ s atmosphere .
If this is indeed the case , it implies that CWW 89Ab is a 36.5 { { M } _ { J } } object that formed via core accretion processes .
Finally , we use our measurement of CWW 89Ab’s orbital eccentricity , improved via these observations , to constrain the tidal quality factors of the brown dwarf and the host star CWW 89A to be Q _ { BD } > 10 ^ { 4.15 } and Q _ { * } > 10 ^ { 9 } , respectively .