(Proposal ID) S11A-140

(PI) McElwain, Michael

(Proposal Title)
Characterizing Exoplanet Atmospheres with Occultation Differential Imaging

(Abstract)
We propose to use HiCIAO simultaneous differential imaging (SDI) to directly 
detect dayside CH_4 absorption in the atmospheres of the transiting exoplanets 
HD 209458b and TrES-2. The unique stability of HiCIAO differential imaging has 
been proven for the case of high contrast imaging, and we plan to extend this 
capability to high precision occultation differential imaging (ODI). The 
detection of dayside emission from transiting exoplanets requires time series 
differential photometry (~10^-4) of the system before, during, and after 
occultation of the exoplanet. The HiCIAO 1.5-1.7mum SDI narrowband filters 
were designed to sample the CH4 absorption feature that is common to wide 
separation and transiting exoplanets. These observations will measure the 
spectral slope of the CH_4 feature to provide a key datapoint which further 
constrains the currently degenerate theoretical models. TrES-2 already has 
K_s-band and Spitzer Space Telescope IRAC 3.6, 4.5, 5.8, and 8.0 mum 
occultation transit depths, but again, HiCIAO CH_4 observations will break 
model degeneracies, improving our understanding of these extreme atmospheric 
conditions.