# What can emission lines tell us?

## TL;DR

This paper reviews how emission lines can be used to diagnose physical conditions in astrophysical objects, discussing empirical methods, modeling, and unresolved questions.

## Contribution

It provides a comprehensive overview of emission line diagnostics, combining empirical approaches with photoionization models and highlighting open questions.

## Key findings

- Emission lines serve as key diagnostics for astrophysical plasmas.
- Photoionization models help interpret emission line data.
- The paper lists useful emission lines and discusses analysis techniques.

## Abstract

1 Generalities 2 Empirical diagnostics based on emission lines 3 Photoionization modelling 4 Pending questions 5 Appendix: Lists of useful lines and how to deal with them