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We present new eclipse observations for one of the hottest "hot Jupiters"WASP-18b, for which previously published data from HST WFC3 and Spitzer haveled to radically conflicting conclusions about the composition of this planet'satmosphere. We measure eclipse depths of $0.15\pm0.02\%$ at $Ks$ and$0.07\pm0.01\%$ at $z'$ bands. Using the VSTAR line-by-line radiative transfercode and both these new observations with previously published data, we derivea new model of the planetary atmosphere. We have varied both the metallicityand C/O ratio in our modelling, and find no need for the extreme metallicitysuggested by Sheppard et al.(2017). Our best fitting models slightlyunderestimate the emission at $z'$ band and overestimate the observed flux at$Ks$-band. To explain these discrepancies, we examine the impact on theplanetary emission spectrum of the presence of several types of hazes whichcould form on the night-side of the planet. Our $Ks$ band eclipse fluxmeasurement is lower than expected from clear atmosphere models and this couldbe explained by a haze particles larger than 0.2 $\mu$m with the opticalproperties of Al$_{2}$O$_{3}$, CaTiO$_{3}$ or MgSiO$_{3}$. We find that $z'$band measurements are important for understanding the contribution ofphotochemical hazes with particles smaller than 0.1 $\mu$m at the top of theatmosphere.

Secondary eclipses of WASP-18b -- Near Infrared observations with the Anglo Australian Telescope, the Magellan Clay Telescope and the LCOGT network