Program: GN-2014A-Q-30

Transmission spectroscopy is a powerful probe of the atmospheres of transiting extrasolar planets, and has recently become accessible from the ground following the discovery of transiting planets with nearby, bright, comparison stars. We have already used GMOS to observe transmission spectroscopy of WASP-29b and HAT-P-32b with differential spectro-photometry, providing strong constraints on their atmospheric compositions. We propose to continue our program by observing two more planetary systems, HAT-P-18b and HAT-P-26b, which will add invaluable information to the currently scarse data on exo-atmospheres. HAT-P-18b and HAT-P-26b are hot, low density planets orbiting relatively small K-dwarfs, and therefore have particularly large variations in transit depth due to the planets' atmospheres. This provides a rare opportunity to probe the atmospheres of Saturn and Neptune mass highly irradiated gas-giants, and may provide the first unambiguous detection of species in their atmospheres. We will use the same proven observational setup, with the R400 grism to provide coverage from ~525-925nm, enabling the search for atomic and molecular species, and determine the dominant physical and chemical processes in their atmospheres. These observations will consolidate Gemini's prominent role in the observation of exoplanet atmospheres.