(Proposal ID) S16A-135

(PI) Masuda, Kento

(Proposal Title)
A Search for a New Class of Circumbinary Planets

(Abstract)
So far, ten circumbinary planets (CBPs), planets orbiting around both of the 
binary stars, have been discovered via the transit observation by the {Kepler} 
space telescope. All of these CBPs have long orbital periods (P_{orb}=50-300 
days) because they orbit around relatively wide binary stars with the binary 
period P_{binary}>7 days, and this feature makes it difficult to characterize 
these planets in detail. In this proposal, we plan to use the Subaru radial 
velocity measurements to search for a new population of CBPs. Our target, 
KOI-7231b, is a transiting CBP candidate we identified in the latest {Kepler} 
data release, whose orbital architecture is totally different from the 
currently known CBPs. Namely, it has an extremely short orbital period 
P_{orb}=4.74 days and orbits around a very tight eclipsing binary with 
P_{binary}=0.82 days. Since theories of close binary formation predict that 
transiting CBPs around such tight binaries should be rare, this candidate, 
if confirmed, challenges the standard view of the CBP formation around close 
binaries. Moreover, revealing this new population of short-period CBPs will 
lead to more discoveries of similar planets in future because they are much 
easier to detect from the ground than such long-period CBPs as discovered in 
the {Kepler} mission.