We present the first spectroscopic study of an exoplanet atmosphere using the EFOSC2 instrument on the New Technology Telescope (NTT). The obtained transmission spectrum of the hot Jupiter WASP-94Ab in the optical wavelength range (3800 - 7140 A) suggests a sodium absorption in the atmosphere of WASP-94Ab, implying a fairly clear atmosphere. In addition, we observe a slope in the blue end of the transmission spectrum, indicating the presence of Rayleigh scattering. 

The WASP-94 system is a binary system, with both bright (Vmag ~ 10) F type stars hosting one confirmed hot Jupiter, where one of them, WASP-94Ab, is transiting. WASP-94Ab orbits its host star in a 4 day misaligned, retrograde orbit at a distance of 0.055 AU. It is an optimal target for transmission spectroscopy as it is reported to have an inflated radius of 1.7 Jupiter radii, a mass of 0.5 Jupiter masses and an equilibrium temperature of 1500 K. However, no atmospheric studies have been published to date. 

These results demonstrate that the NTT/EFOSC2 is able to characterise exoplanet atmospheres, achieving the necessary precisions with errors of less than one atmospheric scale height.