2018ApJ...863..140B

The solar corona shows a distinctive pattern of elemental abundances that is different from that of the photosphere. Low first ionization potential (FIP) elements are enhanced by factors of several. A similar effect is seen in the atmospheres of some solar-like stars, while late-type M stars show an inverse FIP effect. This inverse effect was recently detected on the Sun during solar flares, potentially allowing a very detailed look at the spatial and temporal behavior that is not possible from stellar observations. A key question for interpreting these measurements is whether both effects act solely on low-FIP elements (a true inverse effect predicted by some models), or whether the inverse FIP effect arises because high-FIP elements are enhanced. Here we develop a new diagnostic that can discriminate between the two scenarios, based on modeling of the radiated power loss, and apply the models to a numerical hydrodynamic simulation of coronal loop cooling. We show that when low-/high-FIP elements are depleted/enhanced, there is a significant difference in the cooling lifetime of loops that is greatest at lower temperatures. We apply this diagnostic to a post X1.8 flare loop arcade and inverse FIP region, and show that for this event, low-FIP elements are depleted. We discuss the results in the context of stellar observations, and models of the FIP and inverse FIP effect. We also provide the radiated power-loss functions for the two inverse FIP effect scenarios in machine readable form to facilitate further modeling.