A benchmark study for CHIANTI based on RESIK solar flare spectra

Abstract

Aims. To perform a benchmark analysis for the recent version of the CHIANTI atomic database (v. 5.2) based on high-resolution solar flare X-ray spectra in the range 3.4-6.1 angstrom from the RESIK crystal spectrometer on the CORONAS-F spacecraft.Methods. A C5.8 flare occurring on 2003 February 22 was chosen for analysis. RESIK spectra of this flare include emission lines of He-like and H-like K, Ar, S, and Si, with some dielectronic lines. Initially, two independent plasma diagnostic techniques are employed: an emission measure (EM) loci analysis using the line flux and the line contribution function G(T-e, N-e), and a new method based on continuum fluxes and contribution functions. We further apply a differential emission measure (DEM) analysis, from which CHIANTI synthetic spectra are derived. The continuum from RESIK spectra is checked against simultaneous RHESSI and GOES observations. Comparisons of CHIANTI synthetic spectra with those from the MEKAL code in the 3.4-6.1 angstrom range are also presented.Results. The emitting plasma appears multi-thermal, having one dominant temperature component determined independently from the line and continuum EM loci and DEM analyses. Consistency between line and continuum emissions requires photospheric elemental abundances (Asplund et al. 2005), with a depleted sulphur abundance. With the exception of RESIK channel 4 (5.0-6.1 angstrom), we find overall very good agreement between the calculated and observed intensities. From comparisons with other instruments, RESIK's precision in the continuum level is confirmed to be within the estimated 20% uncertainties in the intensity calibration. We find general agreement between CHIANTI and MEKAL isothermal spectra, but we note that the atomic data for the Si XII and Si XIII ions contained in CHIANTI are more complete.Conclusions. RESIK observations of both lines and continua are suitable for characterising the properties of the flaring plasma such as temperature, emission measure and elemental abundance. These spectra can be used to evaluate any atomic database.