Observed (points) and synthetic (lines) emission spectra for HD 209458b models with Newtonian cooling. The solid line has been calculated from the model presented in Mayne et al. (2014a) and Sect. 3 using ATMO, the dashed line is the synthetic emission spectrum from Fortney et al. (2006), which is based on the models of Cooper & Showman (2005, 2006) using the same Newtonian forcing scheme. The black points are observations from Swain et al. (2008) (●), Crossfield et al. (2012) (▼), Deming et al. (2005) (◄), Zellem et al. (2014) (►), Diamond-Lowe et al. (2014) (■) and Evans et al. (2015) (♦).