Modelling stellar transition regions of FGKM stars with advanced ionisation equilibrium

We employed advanced ionisation equilibrium models developed by Dufresne et al. (2024), which include charge transfer and density effects to study stellar irradiances in the EUV and UV for a sample of stars. Our sample includes \epsilon Eridani (K2 V), \alpha Centauri A (G2 V), Procyon (F5 V), and Proxima Centauri (M5.5 Ve). We remeasured the line fluxes from STIS datasets and used O IV as a density diagnostic to measure the formation pressure of ions in the transition region (TR). Our findings indicate significant improvements in modelling anomalous ions, such as Si IV, C IV and N V, from Li- and Na-like sequences, which produce the strongest lines in UV. We obtained first-time reliable estimates of some stellar chemical abundances in the TR, using a Differential Emission Measure (DEM) modelling. We also obtained significant improvements in the calculated-to-observed flux ratios. These results are compared with available photospheric abundances, demonstrating the effectiveness of our approach to look for evidence of the First Ionisation Potential (FIP) effect, in the TR of our stellar sample. Finally, we compared our results with an analysis of solar TR irradiances in the EUV. Theme(s): The Sun and Cool Stars in the Time Domain, Cool Stars as Stellar Systems