Coronal Elemental Abundance: New Results from Soft X-ray Spectroscopy of the Sun

TL;DR

This study analyzes soft X-ray spectra from multiple space missions to measure how elemental abundances in the solar corona vary with solar activity, revealing a decrease in FIP bias during flares and differences among elements based on FIP.

Contribution

It provides new measurements of coronal elemental abundances across different solar activity levels using direct X-ray spectral data, highlighting dynamic changes during flares.

Findings

FIP bias decreases during X-ray flares, approaching photospheric levels.

Low FIP elements show larger abundance variations than mid FIP elements.

Coronal abundances recover slowly after flare decay.

Abstract

Elemental abundances in the solar corona are known to be different from those observed in the solar photosphere. The ratio of coronal to photospheric abundance shows a dependence on the first ionisation potential (FIP) of the element. We estimate FIP bias from direct measurements of elemental abundances from soft X-ray spectra using data from multiple space missions covering a range of solar activity levels. This comprehensive analysis shows clear evidence for a decrease in FIP bias around maximum intensity of the X-ray flare with coronal abundances briefly tending to photospheric values and a slow recovery as the flare decays. The departure from coronal abundances are larger for the low FIP elements Ca, Fe and Si than for S which have a mid FIP value. These changes in the degree of fractionation might provide inputs to model wave propagation through the chromosphere during flares.