(Proposal ID) S17B-079

(PI) Narita, Norio

(Proposal Title)
Monitoring an Overtaking Double-Transit Event in the TRAPPIST-1 System

(Abstract)
We propose to monitor an overtaking double-transit event of TRAPPIST-1b and 
TRAPPIST-1e on October 23, 2017 with Keck/MOSFIRE and Gemini-North/GMOS 
simultaneously in order to detect/constrain the presence of a planet-planet 
eclipse event. We emphasize that the next overtaking double-transit event is 
an extremely rare opportunity, and there will be no similar chance for the 
planet b and e at least within the next decade. A detection or even non-
detection of the planet-planet eclipse event will give us an insight into the 
mutual inclination of the two planets. A resultant value or lower limit of the 
mutual inclination would become important information when discussing the 
formation/migration mechanism and the dynamical stability of this interesting 
planetary system. We also emphasize the necessity of TWO 8-10m class telescopes
for the proposed observation, since both high photometric precision and high 
time-resolution are critically important to detect or constrain the presence/
absence of a planet-planet eclipse event during the overtaking double-transit 
event, and to avoid any misconception of a planet-planet eclipse event due to 
systematic effects or a starspot crossing event.