Rapoc: the Rosseland and Planck opacity converter. A user-friendly and fast opacity program for Python

We present a novel code that converts the widely-used wavelength-dependent opacities of gaseous species into Rosseland and Planck mean opacities (RPMs). RAPOC (Rosseland and Planck Opacity Converter) is a straightforward and efficient Python code that makes use of ExoMol and DACE data as well as any other user-defined data, provided that it is within the correct format. Furthermore, RAPOC has the useful ability of rapidly interpolating between discrete data points, therefore allowing for a complete incorporation in atmospheric models. 

Whereas RPMs should not be used as a replacement for more rigorous opacity analyses, they have certain benefits. For example, RPMs  allow  one  to  use  Grey  or  semi-Grey  models  when  analysing  gaseous environments;  which  are  simpler,  have  exact  solutions,  and  can  be  used  as benchmarks  for  more  rigorous  approaches. By incorporating the pressure and temperature dependence of RPMs, RAPOC provides a more complex treatment of the mean opacities than what is sometimes used within the literature, notably assuming constant values or adopting simple analytic formulations.  We report  examples  of RAPOC opacities  that  are  incorporated  into  a  semi-Grey  model  to produce the temperature profile of HD 209458 b that is then compared to the realisations of the more rigorous POSEIDON code.

The RAPOC code will provide the exoplanetary community a new tool for atmospheric modelling. For a quick installation in one's machinery, the “pip install rapoc” command can be used.