A library of ATMO forward model transmission spectra for hot Jupiter exoplanets

Abstract

We present a grid of forward model transmission spectra, adopting an isothermal temperature-pressure profile, alongside corresponding equilibrium chemical abundances for 117 observationally significant hot exoplanets (Equilibrium Temperatures of 547-2710 K). This model grid has been developed using a 1D radiative-convectivechemical equilibrium model termed ATMO, with up-to-date high temperature opacities. We present an interpretation of observations of ten exoplanets, including best fit parameters and χ 2 maps. In agreement with previous works, we find a continuum from clear to hazy/cloudy atmospheres for this sample of hot Jupiters. The data for all the 10 planets are consistent with sub-solar to solar C/O ratio, 0.005 to 10 times solar metallicity and water rather than a methane dominated infrared spectra. We then explore the range of simulated atmospheric spectra for different exoplanets, based on characteristics such as temperature, metallicity, C/O-ratio, haziness and cloudiness. We find a transition value for the metallicity between 10 and 50 times solar, which leads to substantial changes in the transmission spectra. We also find a transition value of C/O ratio, from water to carbon species dominated infrared spectra, as found by previous works, revealing a temperature dependence of this transition point ranging from ∼0.56 to ∼1-1.3 for equilibrium temperatures from ∼900 to ∼2600 K. We highlight the potential of the spectral features of HCN and C2H2 to constrain the metallicities and C/O ratios of planets, using JWST observations. Finally, our entire grid (∼460,000 simulations) is publicly available and can be used directly with the JWST simulator PandExo for planning observations.