Measuring relative abundances in the solar corona with optimised linear combinations of spectral lines

TL;DR

This paper introduces an optimized linear combination method of spectral lines to accurately measure FIP biases in the solar corona, bypassing complex DEM inversions and enhancing observational efficiency.

Contribution

The authors develop a novel linear combination approach for FIP bias measurement that is practical, accurate, and independent of DEM inversions, improving coronal abundance analysis.

Findings

Method accurately retrieves FIP bias maps across various DEMs.

Results agree well with traditional DEM-dependent methods.

Provides a fast, reliable tool for coronal abundance studies.

Abstract

Context. Elemental abundances in some coronal structures differ significantly from photospheric abundances, with a dependence on the first ionization potential (FIP) of the element. Measuring these FIP-dependent abundance biases is important for coronal and heliospheric physics. Aims. We aim to build a method for optimal determination of FIP biases in the corona from spectroscopic observations in a way that is in practice independent from Differential Emission Measure (DEM) inversions. Methods. We optimised linear combinations of spectroscopic lines of low-FIP and high-FIP elements so that the ratio of the corresponding radiances yields the relative FIP bias with good accuracy for any DEM in a small set of typical DEMs. Results. These optimised linear combinations of lines allow retrieval of a test FIP bias map with good accuracy for all DEMs in the map. The results also compare well with a FIP bias map obtained from observations using a DEM-dependent method. Conclusions. The method provides a convenient, fast, and accurate way of computing relative FIP bias maps. It can be used to optimise the use of existing observations and the design of new observations and instruments.