MOLECULAR SIGNATURES IN THE NEAR-INFRARED DAYSIDE SPECTRUM OF HD 189733b

We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5 μm using the NICMOS instrument on the Hubble Space Telescope . The emergent spectrum contains significant modulation, which we attribute to the presence of molecular bands seen in absorption. We find that water (H 2 O), carbon monoxide (CO), and carbon dioxide (CO 2 ) are needed to explain the observations, and we are able to estimate the mixing ratios for these molecules. We also find temperature decreases with altitude in the ∼0.01 < P < ∼1 bar region of the dayside near-infrared photosphere and set an upper limit to the dayside abundance of methane (CH 4 ) at these pressures.