Dynamic modeling of coronal abundances during flares on M-dwarf stars

TL;DR

This work investigates how extreme iFIP-like coronal compositions on M-dwarf stars respond to flare heating. Using HYDRAD with time- and space-dependent abundances, the authors simulate two opposite iFIP scenarios (high-FIP enrichment and low-FIP depletion) in a 150 Mm loop subjected to impulsive electron-beam heating, revealing that high-FIP enrichment can produce coronal rain through a localized apex radiative loss peak, while low-FIP depletion suppresses rain by reducing cooling. The study demonstrates that initial elemental composition critically shapes flare cooling and condensation, with implications for interpreting stellar X-ray/EUV light curves and spectra. The results underscore the need to incorporate dynamic abundances in radiative hydrodynamic models of stellar flares and provide a pathway to compare predictions with future observations.

Abstract

Solar atmospheric elemental abundances are now known to vary both in space and time. Dynamic modeling of these changes is therefore necessary to improve the accuracy of radiative hydrodynamic simulations. Recent studies have shown that including spatio-temporal variations in coronal abundances during solar flares leads to the formation of coronal condensations (rain), which are otherwise difficult to create in impulsively heated field aligned hydrodynamic flare models. These simulations start with a solar corona dominated by the first ionization potential (FIP) effect, and evaporate photospheric material into the post-flare loops. We here explore perhaps the most extreme non-solar starting condition for the coronal composition in these simulations: an initial corona dominated by the inverse FIP (iFIP) effect, such as is observed on active M-dwarf stars. We show that a flaring event in a corona enriched with high FIP elements leads to a solution similar to the solar case. Coronal rain is harder to form by this method during flares on M-dwarfs, however, if the corona is depleted of low FIP elements.

Figures (2)

• Figure 1: Electron beam heated loop simulation for the case where high FIP elements are enhanced in the initial corona. Left panel: abundance factor as a function of position along the loop. Time is coded by color (purple$\rightarrow$green$\rightarrow$yellow) in 10 s increments for the first 500 s of the simulation i.e. approximately the initial 17% of the total simulation time shown in the subsequent panels. Middle panel: electron temperature (top) and bolometric radiative losses (bottom) as a function of time along the loop. Right panel: electron density (top) and bulk flow velocity (bottom) as a function of time along the loop. Red/blue velocities indicate flows away from/towards the loop apex. The corona is initially enriched with high FIP elements by a factor of 4 (iFIP effect), but the abundances decrease rapidly towards photospheric values ($f_H$=1.0) due to chromospheric evaporation as the loop heats up. This is similar to the simulation shown in Benavitz2025. A localized peak in $f_H$ forms at the loop apex, which produces an associated increase in radiative losses and a faster cooling time. A coronal rain condensation forms.
• Figure 2: Same as Figure \ref{['fig1']} but for the case where low FIP elements are depleted in the initial corona. The corona is initially depleted of low FIP elements by a factor of 4 (iFIP effect), but the abundances increase rapidly towards photospheric values ($f_L$=1.0) due to chromospheric evaporation as the loop heats up. This is opposite to the simulation shown in Figure \ref{['fig1']} and in Benavitz2025. A localized dip in $f_L$ forms at the loop apex, which produces an associated decrease in radiative losses and a longer cooling time. No coronal rain condensation forms.