(Proposal ID) S11A-023

(PI) Bean, Jacob

(Proposal Title)
Searching for a thermal inversion in the NIR spectrum of the planet XO-2b

(Abstract)
We propose to obtain time-series spectrophotometry in the K-band of a secondary
 eclipse of the transiting hot jupiter exoplanet XO-2b. The purpose of these 
observations is to measure the planet's dayside spectrum. We will use the 
obtained data to definitively determine if the planet has a thermal inversion 
in its atmosphere like a number of other hot jupiter-type planets. The proposed
 study will have important scientific implications, and would also be the first
 demonstration of a method for the ground-based discrimination for the presence
 of thermal inversions in hot jupiters. The observing methodology to be used is
 based on a recently proved technique for obtaining ground-based eclipse 
spectroscopy that yields data as good as the best data that can be obtained 
using space telescopes. The key elements of the technique are simultaneous 
observation of a reference star and using very wide slits to avoid time-
variable and differential slit losses. This investigation can best be carried 
out using Subaru because the MOIRCS instrument is the only near-infrared 
spectrograph on a large telescope that is suitable for the technique.