Signs of sulfur fractionation under high magnetic field strength.

Abstract

Sulfur, with a first ionization potential (FIP) of 10.36 eV, lies at the boundary between low- and high-FIP elements, making it particularly sensitive to fractionation processes in the solar atmosphere. Sulfur exhibits variable behaviour across solar environments, with coronal remote sensing studies often observing it as a high-FIP element, while in situ measurements sometimes detect low-FIP-like enhancement. Sulfur also exhibits variable behaviour during flares and magnetic restructuring. To understand sulfur's variations, we quantify how sulfur's FIP bias depends on potential field source surface (PFSS)-derived loop properties. We analyse nine Hinode/EUV Imaging Spectrometer (EIS) raster observations using four diagnostic line pairs (Si x 258.37 Å /S x 264.23 Å, S xi 188.68 Å /Ar xi 188.81 Å, Ca xiv 193.87 Å /Ar xiv 194.40 Å and Fe xvi 262.98 Å /S xiii 256.69 Å), with FIP biases derived using differential emission measures (DEM) calculated via regularized inversion. Our results show that the abundance of low-FIP elements, including sulfur, decreases above approximately 150 G relative to the high-FIP element Ar, while showing no dependence on loop length. This provides evidence that FIP fractionation is modulated by the mean magnetic field strength of the coronal loops. This article is part of the Theo Murphy meeting issue 'Solar atmospheric abundances in space and time'.