Measuring relative abundances in the solar corona with optimised linear combinations of spectral lines
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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2019
- DOI:
- 10.1051/0004-6361/201834735
- arXiv:
- arXiv:1910.02886
- Bibcode:
- 2019A&A...632A..20Z
- Keywords:
-
- techniques: spectroscopic;
- Sun: abundances;
- Sun: corona;
- Sun: UV radiation;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- 13 pages, 14 figures