tokens: of C/O is roughly uniform, unlike for unconstrained chemistry where it is double-peaked (Line et al. 2013 ). In chemical equilibrium, specifying the elemental abundances allows all of the molecular abundances to be computed, with no parametric freedom, given a temperature and pressure. We are agnostic about the terms “cloud” and “haze” and use them interchangeably for this study. 7 7 These terms are either used to distinguish between size (Earth science convention) or formation origin (planetary science convention), and there is no consensus within the exoplanet community on their usage. We implement the simplified cloud model introduced by Lee et al. ( 2013 ) and used by Lavie et al. ( 2017 ), which describes a monodisperse population of spherical cloud particles with radii , cloud volume mixing ratio and a single composition (represented by the parameter Q 0 ). Refractory and volatile cloud species have and ∼10, respectively. This cloud model accommodates both small and large particles, and correctly reproduces the limits of Rayleigh and gray scattering. It is based on the notion that curves of the extinction coefficient have a roughly universal shape (Pierrehumbert 2010 ). 3. Results We begin by presenting a pair of retrieval models that make the common assumption of log-uniform priors (Figure 3 ). For the measured emission spectrum of WASP-12b, we use the published data of Stevenson et al. ( 2014 ) as stated in their Table 3. For the model with unconstrained chemistry, we set log-uniform priors on the six mixing ratios. For the model with equilibrium chemistry, we set log-uniform priors on the elemental abundances of carbon, oxygen, and nitrogen. As an improvement over the work of Stevenson et al. ( 2014 ), we include clouds in our analysis as part of the retrieval (i.e., the cloud parameters are not fixed to preset values). The other parameters also have log-uniform priors, except for Q 0 , which has a (linearly) uniform prior. Figure 3. Posterior distributions of fitting parameters for cloudy retrieval models with unconstrained chemistry (top panel) and equilibrium chemistry (bottom panel) with log-uniform priors. has physical units of m 2 kg −1 , while is given in m. The rest of the parameters are dimensionless. In Figure 3 , the first thing to notice is that the cloud parameters display degeneracies that match our physical intuition: the mixing ratios are degenerate with cloud composition, particle radius, and number density. In particular, it is possible to set bounds on the cloud particle radius, but the cloud composition is essentially—and unsurprisingly—unconstrained. When we include only CO, CO 2 , CH 4 , and H 2 O in the retrieval, we reproduce the result of Line et al. ( 2014 ) and Stevenson et al. ( 2014 ) that unrealistically high abundances for CO 2 are obtained (not shown). (Heng Lyons 2016 have previously elucidated this implausibility using validated analytical formulae.) Such high abundances of CO 2 drive the
ner_tags: O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-TextGarbage I-TextGarbage O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O