Cthulhu: An Open Source Molecular and Atomic Cross Section Computation Code for Substellar Atmospheres

TL;DR

Cthulhu is an open-source Python package that efficiently computes molecular and atomic cross sections for exoplanet and brown dwarf atmospheric modeling, supporting large datasets and providing educational resources.

Contribution

It introduces a versatile, easy-to-use Python tool that automates cross section calculations from line lists, suitable for both small and large datasets, with comprehensive tutorials.

Findings

Supports line lists with up to billions of lines

Runs efficiently on laptops and clusters

Includes educational Jupyter notebooks

Abstract

Atmospheric studies of exoplanets and brown dwarfs are a cutting-edge and rapidly evolving area of astrophysics research. Calculating models of exoplanet or brown dwarf spectra requires knowledge of the wavelength-dependent absorption of light (cross sections) by the molecules and atoms in the atmosphere. Here we introduce Cthulhu, a pure Python package that rapidly calculates cross sections from atomic and molecular line lists. Cthulhu includes modules to automatically download molecular line lists from online databases (e.g. ExoMol and HITRAN) and compute cross sections on a user-specified temperature, pressure, and wavenumber grid. Cthulhu requires only CPUs and can run on a user's laptop (for smaller line lists with < 100 million lines) or on a large cluster in parallel (for many billion lines). Cthulhu includes in-depth Jupyter tutorials in the online documentation. Finally, Cthulhu can be used as an educational tool to demystify the process of making cross sections for atmospheric models.