FIGURE 2. A comparison of the observations of primary transit with a simulated infrared and optical transmission spectrum.
From the following article:
Water vapour in the atmosphere of a transiting extrasolar planet
Giovanna Tinetti, Alfred Vidal-Madjar, Mao-Chang Liang, Jean-Philippe Beaulieu, Yuk Yung, Sean Carey, Robert J. Barber, Jonathan Tennyson, Ignasi Ribas, Nicole Allard, Gilda E. Ballester, David K. Sing & Franck Selsis
Nature 448, 169-171(12 July 2007)
doi:10.1038/nature06002
The transmission spectrum is here modelled from 0.5 to 25 
m (grey trace). We assumed a water mixing ratio of 
5 
10-4 and a cold terminator temperature–pressure profile. The observations are indicated with black triangles and error bars at 1
. Absorptions due to alkali metals and water are unlikely to be the cause of the extra absorption observed at visible wavelengths: the mean absorption over the 0.5–1 m band is significantly less than the measured value. Star spots or optically thick condensates/hazes would be a good explanation.