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The 2023 release of Cloudy

Marios Chatzikos, Stefano Bianchi, Francesco Camilloni, Priyanka Chakraborty, Chamani M. Gunasekera, Francisco Guzmán, Jonathan S. Milby, Arnab Sarkar, Gargi Shaw, Peter A. M. van Hoof, Gary J. Ferland

TL;DR

The paper presents Cloudy’s 2023 release (C23), detailing an annual, git-driven release cadence and substantial upgrades to atomic and molecular data, notably Chianti v10, updated H-like/He-like collisional rates, and the LAMDA/UDfA/KiDA data suites. It also describes significant X-ray capabilities enhancements for upcoming XRISM and Athena missions, including microcalorimeter readiness and refined inner-shell physics, along with broad infrastructure upgrades from C++11 porting to improved parsing, I/O, and SED grid handling. The work emphasizes improved spectral predictions across UV–X-ray regimes, with richer Fe II modeling, refined K$lpha$ energies, enhanced H$_2$ chemistry, and dust physics via Jenkins depletion patterns. Together, these changes advance Cloudy’s accuracy, performance, and applicability to high-resolution astrophysical spectra, particularly in the X-ray, while positioning the code for future developments in time-dependent radiative transfer and atomic data curation in the Stout database.

Abstract

We describe the 2023 release of the spectral synthesis code Cloudy. Since the previous major release, migrations of our online services motivated us to adopt git as our version control system. This change alone led us to adopt an annual release scheme, accompanied by a short release paper, the present being the inaugural. Significant changes to our atomic and molecular data have improved the accuracy of Cloudy predictions: we have upgraded our instance of the Chianti database from version 7 to 10; our H- and He-like collisional rates to improved theoretical values; our molecular data to the most recent LAMDA database, and several chemical reaction rates to their most recent UDfA and KiDA values. Finally, we describe our progress on upgrading Cloudy's capabilities to meet the requirements of the X-ray microcalorimeters aboard the upcoming XRISM and Athena missions, and outline future development that will make Cloudy of use to the X-ray community.

The 2023 release of Cloudy

TL;DR

The paper presents Cloudy’s 2023 release (C23), detailing an annual, git-driven release cadence and substantial upgrades to atomic and molecular data, notably Chianti v10, updated H-like/He-like collisional rates, and the LAMDA/UDfA/KiDA data suites. It also describes significant X-ray capabilities enhancements for upcoming XRISM and Athena missions, including microcalorimeter readiness and refined inner-shell physics, along with broad infrastructure upgrades from C++11 porting to improved parsing, I/O, and SED grid handling. The work emphasizes improved spectral predictions across UV–X-ray regimes, with richer Fe II modeling, refined K energies, enhanced H chemistry, and dust physics via Jenkins depletion patterns. Together, these changes advance Cloudy’s accuracy, performance, and applicability to high-resolution astrophysical spectra, particularly in the X-ray, while positioning the code for future developments in time-dependent radiative transfer and atomic data curation in the Stout database.

Abstract

We describe the 2023 release of the spectral synthesis code Cloudy. Since the previous major release, migrations of our online services motivated us to adopt git as our version control system. This change alone led us to adopt an annual release scheme, accompanied by a short release paper, the present being the inaugural. Significant changes to our atomic and molecular data have improved the accuracy of Cloudy predictions: we have upgraded our instance of the Chianti database from version 7 to 10; our H- and He-like collisional rates to improved theoretical values; our molecular data to the most recent LAMDA database, and several chemical reaction rates to their most recent UDfA and KiDA values. Finally, we describe our progress on upgrading Cloudy's capabilities to meet the requirements of the X-ray microcalorimeters aboard the upcoming XRISM and Athena missions, and outline future development that will make Cloudy of use to the X-ray community.
Paper Structure (34 sections, 6 equations, 10 figures, 1 table)

This paper contains 34 sections, 6 equations, 10 figures, 1 table.

Table of Contents

  1. Introduction
  2. Online Migration
  3. Migration of nublado.org
  4. User Forum Migration
  5. Atomic Physics
  6. Upgrade to Chianti version 10
  7. Updates to the Stout database
  8. Fe II
  9. K$\alpha$ energies
  10. Inner shell energies
  11. $\ell$-changing collisions
  12. The importance of a correct number of resolved levels: printing $\ell$-changing critical densities
  13. n-changing collisions
  14. Masing of H$n\alpha$ lines
  15. Molecular Data
  16. ...and 19 more sections

Figures (10)

  • Figure 1: Energy level structure of the $\hbox{\rm Fe {\sc ii}}$ models available with Cloudy. From left to right, the atomic datasets are those of 1999ApJS..120..101V, 2015ApJ...808..174B, 2018PhRvA..98a2706T, and 2019MNRAS.483..654S. The $\hbox{\rm H {\sc i}}$ and $\hbox{\rm Fe {\sc ii}}$ ionization limits, the Ly$\alpha$ energy, an important source of photoexcitation for $\hbox{\rm Fe {\sc ii}}$, and the thermal energy corresponding to 10$^4$ K are also indicated. Adapted from CloudyFeII2021.
  • Figure 2: Comparison between the observed $\hbox{\rm Fe {\sc ii}}$ UV template of 2001ApJS..134....1V and the $\textsc{Cloudy}$ predicted $\hbox{\rm Fe {\sc ii}}$ UV spectrum with V$_{\rm turb}$ = 100 km/s.
  • Figure 3: The absolute value of the difference between NIST and Cloudy K$\alpha$ energies versus K$\alpha$ energies for H-like ions of elements between $6 \leq Z \leq 30$. Red triangles show the difference between energies in the current version (as of C17.03) of Cloudy and NIST, while green circles show the same difference for previous versions of Cloudy (from $\sim$2005 to C17.02).
  • Figure 4: Visually co-added Chandra MEG $\pm1$ order spectra of the HMXB Vela X-1 at the orbital phase $\phi_{orb}=0.75$2021AA...648A.105A. Top: Best fit model with Cloudy (grey solid line), using the improved energies for the Si fluorescence lines, available in C23. The specific contributions of each gas component are labeled (red dashed line and blue dot-dashed line), together with the best-fit parameters and 90% confidence level uncertainties 2021RNAAS...5..149C. Bottom: As above, but with the previous version of Cloudy, C17. The low ionization component is here labeled in green, together with the adopted Si K$\alpha$ lines 1993AAS...97..443K. For ease of comparison, the improved energies from 2016ApJ...830...26H are in blue, as in the top panel. Adapted from 2021RNAAS...5..149C.
  • Figure 5: Comparison of critical densities from equation \ref{['eq:critdens']} with $\ell$-changing collisions from PS-M20 with the results of figure 4 of PengellySeaton1964. We have chosen a pure hydrogen gas at electron temperature $T=10000$K and electron density $n_e=10^4{\rm cm^{-3}}$. The agreement is complete.
  • ...and 5 more figures