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Project Progress

In this reporting period, we have focused on analyzing three exoplanets in primary transit (WASP-12b, WASP-17b, and WASP-19b) for signs of water vapor and other molecules in their atmospheres. We analyzed the data for a single primary transit of each planet with a new methodology that allows us to correct for channel– or wavelength–dependent instru-mental effects by utilizing the band-integrated time series and measurements of the drift of the spectra on the detector over time. We have developed a data reduction pipeline and analysis methodology that produces spectra with precision close to the theoretical noise floor for individual spectral bins. The final results are broadly consistent with the presence of absorption at 1.4 µm, most likely due to water, but the amplitude of the absorption was less than that expected based on previous observations with Spitzer – possibly due to hazes absorbing in the Near InfraRed (NIR) or to non-solar compositions.

For WASP-17b the water signal was clear, but for the two other planets the degeneracy of models with different compositions and temperature structures combined with the low amplitude of any features in the data precluded our ability to place unambiguous constraints on the atmospheric composition. More sensitive observations with WFC3 and/or a comprehensive multi-wavelength analysis are planned. A paper detailing our efforts and results has been published (Mandell et al. 2013), and some of our data analysis strategies were also incorporated into a related publication (Deming et al. 2013).