Patterns of X-ray Line Emission

Title:		Patterns of X-ray Line Emission Variability as Observed by the RESIK Bragg Spectrometer
Authors:		J. SYLWESTER, B. SYLWESTER J.L. Culhane, G.A. Doschek, V.N. Oraevsky, K.J.H.Phillips
Abstract:		RESIK is a unique Bragg bent crystal spectrometer operating continuously since August 2001. By now, it has collected ~ 10 GB of solar flare and active region spectra in a very much unexplored spectral region between 3.2 Å and 6.1 Å. In this paper we present a number of representative observations covering periods of various solar activity: from the most active level (M+ flares) to exceptionally quiet corona. We present also a tentative list of the spectral features observed. In the wavelength range observed by RESIK there are a number of strong emission lines corresponding to H- and He-like resonance transitions of Si, S, Ar and K ions. These lines are formed by thermal plasma of temperature between 5 and 50 MK, and therefore their analysis reveal the distribution of hot plasma over this interval. RESIK sees lines from a number of different elements, so it is possible to do abundance analyses. The elements concerned have a wide range of first ionisation potentials (FIPs) so it has been possible to examine the dependence of coronal or flare abundances on FIP. We have observed substantial variations of the K/Ar line ratio, and respective line/continuum ratios, which can be best explained by allowing for changes in the chemical composition of the coronal plasma.