The 2025 Release of Cloudy

TL;DR

The 2025 Cloudy release introduces enhanced physics, improved spectral resolution, updated databases, and expanded molecular networks, significantly advancing spectral synthesis capabilities for astrophysical and exoplanetary research.

Contribution

This release provides major updates to Cloudy, including resolving Lyman alpha lines, updating ionization data, expanding molecular networks, and preparing for future observatory data analysis.

Findings

Improved spectral resolution for X-ray applications.

Enhanced molecular and chemical modeling capabilities.

Updated databases for more accurate simulations.

Abstract

We present the 2025 release of the spectral synthesis code Cloudy, highlighting significant enhancements to the scope and accuracy of the physics which have been made since the previous release. A major part of this development involves resolving the Lyman $\alpha$ line into $j$-resolved fine-structure doublets, making Cloudy of use to the X-ray community. On this front, we have also updated inner-shell ionization line energies and incorporated the 1 keV feature commonly observed in X-ray binaries. Additionally, we update our in-house database, Stout, for the carbon isoelectronic sequence, improving Cloudy microphysical calculations for all wavelengths. We have also extended the molecular network by adding new silicon-bearing species, titanium-related reactions, and phosphorus-containing molecules, enhancing Cloudy's ability to model the complex chemistry relevant to rapidly growing field of exoplanet atmospheres. Finally, we outline future developments aimed at maximizing the scientific return from the current and upcoming generation of observatories, including XRISM, JWST, Roman, the Habitable Worlds Observatory (HWO) and NewAthena.