Monte Carlo Markov Chain DEM reconstruction of isothermal plasmas

TL;DR

This study evaluates the effectiveness of the MCMC technique in reconstructing isothermal plasmas from spectral data, highlighting its limitations in resolution, sensitivity to atomic data uncertainties, and ability to distinguish thermal structures.

Contribution

It provides a comprehensive assessment of MCMC DEM reconstruction capabilities, including its resolution limits and effects of data uncertainties, advancing understanding of plasma diagnostics.

Findings

MCMC can retrieve isothermal plasmas with a resolution of Delta log T = 0.05.

Two close isothermal components are distinguishable if separated by Delta log T = 0.2 or more.

Atomic data uncertainties significantly impact temperature and DEM peak values.

Abstract

In this paper, we carry out tests on the Monte Carlo Markov Chain (MCMC) technique with the aim of determining: 1) its ability to retrieve isothermal plasmas from a set of spectral line intensities, with and without random noise; 2) to what extent can it discriminate between an isothermal solution and a narrow multithermal distribution; and 3) how well it can detect multiple isothermal components along the line of sight. We also test the effects of 4) atomic data uncertainties on the results, and 5) the number of ions whose lines are available for the DEM reconstruction. We find that the MCMC technique is unable to retrieve isothermal plasmas to better than Delta log T = 0.05. Also, the DEM curves obtained using lines calculated with an isothermal plasma and with a Gaussian distribution with FWHM of log T = 0.05 are very similar. Two near-isothermal components can be resolved if their temperature separation is Delta log T = 0.2 or larger. Thus, DEM diagnostics has an intrinsic resolving power of log T = 0.05. Atomic data uncertainties may significantly affect both temperature and peak DEM values, but do not alter our conclusions. The availability of small sets of lines also does not worsen the performance of the MCMC technique, provided these lines are formed in a wide temperature range. Our analysis shows the present limitations in our ability to identify the presence of strictly isothermal plasmas in stellar and solar coronal spectra.