Volume 632, December 2019
|Number of page(s)||11|
|Published online||21 November 2019|
Measuring relative abundances in the solar corona with optimised linear combinations of spectral lines
Institut d’Astrophysique Spatiale, CNRS/Université Paris-Sud, Université Paris-Saclay, Bâtiment 121, Université Paris-Sud, 91405 Orsay Cedex, France
Accepted: 30 September 2019
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.
Key words: techniques: spectroscopic / Sun: abundances / Sun: corona / Sun: UV radiation
© N. Zambrana Prado and É. Buchlin 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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