# Actinide opacities for modeling the spectra and light curves of kilonovae

**Authors:** C. J. Fontes, C. L. Fryer, R. T. Wollaeger, M. R. Mumpower, T. M. Sprouse  
**arXiv:** [2209.12759](https://arxiv.org/abs/2209.12759)  
**Date:** 2022-09-26  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2209.12759v1/

## Key points

- C.J. Fontes and colleagues conducted a study on actinide opacities for use in modeling kilonova (KN) light curves and spectra
- The researchers used the configuration-interaction approach to generate detailed, fine-structure line features
- Opacity tables for 14 actinide elements were pre-computed over a grid of relevant temperatures and densities using a line-binned treatment
- These tabular opacities will be made publicly available for general usage in KN modeling
- The researchers explored the sensitivity of light curves and spectra to different actinide abundance distributions predicted by different nuclear theories, as well as to different choices of ejecta mass and velocity
- Very little sensitivity was found to the two considered distributions, indicating that opacities for actinides with $Z \ge 99$ do not contribute strongly
- A single actinide element, protactinium, produces faint spectral features in the far infrared at late times (5-7 days post merger)
- The choice of ejecta mass and velocity has the most significant effect on KN emission for this study

## Summary

In their recent study, C. J. Fontes and colleagues extend previous ab initio calculations of lanthanide opacities to include a complete set of actinide opacities for use in the modeling of kilonova (KN) light curves and spectra. The researchers generate detailed, fine-structure line features using the configuration-interaction approach, which display similar trends to those observed for lanthanide opacities, such as lighter actinides producing higher opacity than heavier ones for relevant conditions in the dynamical ejecta. To pre-compute opacity tables for 14 actinide elements $(89 \le Z \le 102)$ over a grid of relevant temperatures and densities, a line-binned treatment is employed. These tabular opacities will be made publicly available for general usage in KN modeling. The researchers demonstrate the usefulness of these opacities in KN simulations by exploring the sensitivity of light curves and spectra to different actinide abundance distributions predicted by different nuclear theories, as well as to different choices of ejecta mass and velocity. They find very little sensitivity to the two considered distributions, indicating that opacities for actinides with $Z \ge 99$ do not contribute strongly. However, they note that a single actinide element, protactinium, produces faint spectral features in the far infrared at late times (5-7 days post merger). Overall, the researchers find that the choice of ejecta mass and velocity has the most significant effect on KN emission for this study. With these new findings on actinide opacities and their impact on KN modeling, future studies can refine our understanding of these phenomena and provide more accurate predictions about their behavior.