We use Kepler short cadence light curves to constrain the oblateness of planet candidates in the Kepler sample .
The transits of rapidly rotating planets that are deformed in shape will lead to distortions in the ingress and egress of their light curves .
We report the first tentative detection of an oblate planet outside of the solar system , measuring an oblateness of 0.22 _ { -0.11 } ^ { +0.11 } for the 18 M _ { J } mass brown dwarf Kepler 39b ( KOI-423.01 ) .
We also provide constraints on the oblateness of the planets ( candidates ) HAT-P-7b , KOI-686.01 , and KOI-197.01 to be < 0.067 , < 0.251 , and < 0.186 , respectively .
Using the Q ^ { \prime } -values from Jupiter and Saturn , we expect tidal synchronization for the spins of HAT-P-7b , KOI-686.01 and KOI-197.01 , and for their rotational oblateness signatures to be undetectable in the current data .
The potentially large oblateness of KOI-423.01 ( Kepler 39b ) suggests that the Q ^ { \prime } -value of the brown dwarf needs to be two orders of magnitude larger than that of the solar system gas giants to avoid being tidally spun-down .