TAU-REX I: A NEXT GENERATION RETRIEVAL CODE FOR EXOPLANETARY ATMOSPHERES

Abstract

Spectroscopy of exoplanetary atmospheres has become a well established method\nfor the characterisation of extrasolar planets. We here present a novel inverse\nretrieval code for exoplanetary atmospheres. TauRex (Tau Retrieval for\nExoplanets) is a line-by-line radiative transfer fully Bayesian retrieval\nframework. TauRex includes the following features: 1) the optimised use of\nmolecular line-lists from the Exomol project; 2) an unbiased atmospheric\ncomposition prior selection, through custom built pattern recognition software;\n3) the use of two independent algorithms to fully sample the Bayesian\nlikelihood space: nested sampling as well as a more classical Markov Chain\nMonte Carlo approach; 4) iterative Bayesian parameter and model selection using\nthe full Bayesian Evidence as well as the Savage-Dickey Ratio for nested\nmodels, and 5) the ability to fully map very large parameter spaces through\noptimal code parallelisation and scalability to cluster computing. In this\npublication we outline the TauRex framework and demonstrate, using a\ntheoretical hot-Jupiter transmission spectrum, the parameter retrieval and\nmodel selection. We investigate the impact of Signal-to-Noise and spectral\nresolution on the retrievability of individual model parameters, both in terms\nof error bars on the temperature and molecular mixing ratios as well as its\neffect on the model's global Bayesian evidence.\n