Welcome to ExoComp!
Many different retrieval codes exist, each with different methods for quantifying atmospheric compositions. In general, chemical equilibrium retrievals quote a metallicity and C/O, but the way in which these are defined varies. For some codes, metallicity is parameterized by O/H, while C/O adjusts the C/H ratio. But in other codes, it is the opposite!
Exocomp is a toolkit with functions and utilities for normalizing measurements from different retrievals of exoplanets and brown dwarfs. Features include:
Conversions between volume mixing ratio and mass fraction (and vice versa).
Conversions in bulk abundances between different definitions of solar composition (or between definitions of host star abundances).
Conversions from metallicity, C/O, and refractory-to-volatile ratios to elemental abundance ratios.
Fitting of metallicity, C/O, and refractory-to-volatile ratios to sets of atomic and molecular abundances.
Calculation of equilibrium molecular abundances for desired species given metallicity, C/O ratio, temperature, and pressure.
All of the above can be easily done with different solar (or stellar) abundance definitions. Available solar abundance defintions include:
Lodders+ 2025
Lodders+ 2020
Lodders+ 2010
Asplund+ 2021
Asplund+ 2009
Asplund+ 2005
Caffau+ 2011
You can find the code on Github here.
We also have compiled The Library of Exoplanet Atmospheric Composition Measurements (LExACoM) Table, which lists metallicity, C/O, and refractory-to-volatile measurements from retrievals of exoplanets from direct, eclipse, and transmission spectroscopy.
Check out the paper, now in AJ here.
Installation: