Fe XXIV Research Articles

Application of relativistic distorted-wave method to electron-impact excitation of highly charged Fe XXIV ion embedded in weakly coupled plasmas

The process of excitation of highly charged Fe XXIV ion embedded in weakly coupled plasmas by electron impact is studied, together with the subsequent radiative decay. For the target structure, the calculation is performed using the multiconfiguration Dirac-Hartree-Fock method incorporating the Debye-Hückel potential for the electron-nucleus interaction. Fine-structure levels of the 1s22p and 1s2s2p configurations and the transition properties among these levels are presented over a wide range of screening parameters. For the collision dynamics, the distorted-wave method in the relativistic frame is adopted to include the effect of plasma background, in which the interparticle interactions in the system are described by screened interactions of the Debye-Hückel type. The continuum wave function of the projectile electron is obtained by solving the modified Dirac equations. The influence of plasma strength on the cross section, the linear polarization, and the angular distribution of x-ray photon emission are investigated in detail. Comparison of the present results with experimental data and other theoretical predictions, when available, is made.

Spectroscopic Observations of a Current Sheet in a Solar Flare

Abstract The current sheet is believed to be the region of energy dissipation via magnetic reconnection in solar flares. However, its properties, for example, the dynamic process, are not fully understood. Here, we report a current sheet in a solar flare (SOL2017-09-10T16:06) that was clearly observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory as well as the EUV Imaging Spectrometer on Hinode. The high-resolution imaging and spectroscopic observations show that the current sheet is mainly visible in high-temperature (>10 MK) passbands, particularly in the Fe xxiv 192.03 Å line with a formation temperature of ∼18 MK. The hot Fe xxiv 192.03 Å line exhibits very large nonthermal velocities up to 200 km s−1 in the current sheet, suggesting that turbulent motions exist there. The largest turbulent velocity occurs at the edge of the current sheet, with some offset with the strongest line intensity. At the central part of the current sheet, the turbulent velocity is negatively correlated with the line intensity. From the line emission and turbulent features we obtain a thickness in the range of 7–11 Mm for the current sheet. These results suggest that the current sheet has internal fine and dynamic structures that may help the magnetic reconnection within it proceed efficiently.

DEPARTURE OF HIGH-TEMPERATURE IRON LINES FROM THE EQUILIBRIUM STATE IN FLARING SOLAR PLASMAS

ABSTRACT The aim of this study is to clarify if the assumption of ionization equilibrium and a Maxwellian electron energy distribution is valid in flaring solar plasmas. We analyze the 2014 December 20 X1.8 flare, in which the Fe xxi 187 Å, Fe xxii 253 Å, Fe xxiii 263 Å, and Fe xxiv 255 Å emission lines were simultaneously observed by the EUV Imaging Spectrometer on board the Hinode satellite. Intensity ratios among these high-temperature Fe lines are compared and departures from isothermal conditions and ionization equilibrium examined. Temperatures derived from intensity ratios involving these four lines show significant discrepancies at the flare footpoints in the impulsive phase, and at the looptop in the gradual phase. Among these, the temperature derived from the Fe xxii/Fe xxiv intensity ratio is the lowest, which cannot be explained if we assume a Maxwellian electron distribution and ionization equilibrium, even in the case of a multithermal structure. This result suggests that the assumption of ionization equilibrium and/or a Maxwellian electron energy distribution can be violated in evaporating solar plasma around 10 MK.

Searching for X-ray sources in nearby late-type galaxies with low-star formation rates

Late type non-starburst galaxies have been shown to contain X-ray emitting objects, some being ultraluminous X-ray sources. We report on XMM-Newton observations of 11 nearby, late-type galaxies previously observed with the Hubble Space Telescope (HST) in order to find such objects. We found 18 X-ray sources in or near the optical extent of the galaxies, most being point-like. If associated with the corresponding galaxies, the source luminosities range from $2 \times 10^{37}$ erg s$^{-1}$ to $6 \times 10^{39}$ erg s$^{-1}$. We found one ultraluminous X-ray source, which is in the galaxy IC 5052, and one source coincident with the galaxy IC 4662 with a blackbody temperature of $0.166 \pm 0.015$ keV that could be a quasi-soft source or a quiescent neutron star X-ray binary in the Milky Way. One X-ray source, XMMU J205206.0$-$691316, is extended and coincident with a galaxy cluster visible on an HST image. The X-ray spectrum of the cluster reveals a redshift of $z = 0.25 \pm 0.02$ and a temperature of 3.6$\pm$0.4 keV. The redshift was mainly determined by a cluster of Fe XXIV lines between the observed energy range $0.8-1.0$ keV.

FLARE FOOTPOINT REGIONS AND A SURGE OBSERVED BYHINODE/EIS,RHESSI, ANDSDO/AIA

The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft observed flare footpoint regions coincident with a surge for a M3.7 flare observed on 25 September 2011 at N12 E33 in active region 11302. The flare was observed in spectral lines of O VI, Fe X, Fe XII, Fe XIV, Fe XV, Fe XVI, Fe XVII, Fe XXIII and Fe XXIV. The EIS observations were made coincident with hard X-ray bursts observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Overlays of the RHESSI images on the EIS raster images at different wavelengths show a spatial coincidence of features in the RHESSI images with the EIS upflow and downflow regions, as well as loop-top or near-loop-top regions. A complex array of phenomena was observed including multiple evaporation regions and the surge, which was also observed by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) telescopes. The slit of the EIS spectrometer covered several flare footpoint regions from which evaporative upflows in Fe XXIII and Fe XXIV lines were observed with Doppler speeds greater than 500 km s$^{-1}$. For ions such as Fe XV both evaporative outflows (~200 km s$^{-1}$) and downflows (~30-50 km s$^{-1}$) were observed. Non-thermal motions from 120 to 300 km s$^{-1}$ were measured in flare lines. In the surge, Doppler speeds are found from about 0 to over 250 km s$^{-1}$ in lines from ions such as Fe XIV. The non-thermal motions could be due to multiple sources slightly Doppler-shifted from each other or turbulence in the evaporating plasma. We estimate the energetics of the hard X-ray burst and obtain a total flare energy in accelerated electrons of $\geq7\times10^{28}$ ergs. This is a lower limit because only an upper limit can be determined for the low energy cutoff to the electron spectrum. We find that detailed modeling of this event would require a multi-threaded model due to its complexity.

Direct observation of the energy release site in a solar flare by SDO/AIA, Hinode/EIS, and RHESSI

We present direct evidence for the detection of the main energy release site in a non-eruptive solar flare, SOL2013-11-09T06:38UT. This GOES C2.7 event was characterised by two flaring ribbons and a compact, bright coronal source located between them, which is the focus of our study. We use imaging from SDO/AIA, and imaging spectroscopy from RHESSI to characterise the thermal and non-thermal emission from the coronal source, and EUV spectroscopy from the Hinode/EIS, which scanned the coronal source during the impulsive peak, to analyse Doppler shifts in Fe XII and Fe XXIV emission lines, and determine the source density. The coronal source exhibited an impulsive emission lightcurve in all AIA filters during the impulsive phase. RHESSI hard X-ray images indicate both thermal and non-thermal emission at the coronal source, and its plasma temperature derived from RHESSI imaging spectroscopy shows an impulsive rise, reaching a maximum at 12-13 MK about 10 seconds prior to the hard X-ray peak. High redshifts associated with this bright source indicate downflows of 40-250 km/s at a broad range of temperatures, interpreted as loop shrinkage and/or outflows along the magnetic field. Outflows from the coronal source towards each ribbon are also observed by AIA images at 171, 193, 211, 304 and 1600 A. The electron density of the source obtained from a Fe XIV line pair is $10^{11.50}$ which is collisionally thick to electrons with energy up to 45-65 keV, responsible for the source's non-thermal X-ray emission. We conclude that the bright coronal source is the location of the main release of magnetic energy in this flare, with a geometry consistent with component reconnection between crossing, current-carrying loops. We argue that the energy that can be released via reconnection, based on observational estimates, can plausibly account for the non-thermal energetics of the flare.

Electron temperature and density characterization using L-shell spectroscopy of laser irradiated buried iron layer targets

Uniform high density plasmas of different materials with properties relevant to the interior of stars and to inertial fusion can be created by laser irradiation of targets containing a buried layer of the material. Buried layer targets also enable the diagnosis of hot and thermal electron, x-ray and ion heating of targets. In this paper, L-emission spectroscopy from an iron layer (thickness 77 nm) encased in an otherwise plastic target (of thickness 240 nm–1.36 μm on the laser side) is irradiated by 0.53 μm wavelength, 2 ps duration laser pulses at irradiances of 1017–1018 Wcm−2. The relative iron L-emission from Li-like Fe XXIV to Ne-like Fe XVII is used to diagnose the plasma conditions of temperature and density in the iron layer. As the upper quantum states of the L-emission lines are in local thermodynamic equilibrium, line intensity ratios depend on both electron temperature and density, which—we show—enables the simultaneous measurement of both electron temperature and density by considering several line intensity ratios. We also show that hot electron target heating and the value of thermal flux limited heat conduction can be evaluated from the relative intensity of iron lines.

PLASMA DYNAMICS ABOVE SOLAR FLARE SOFT X-RAY LOOP TOPS

We measure non-thermal motions in flare loop tops and above the loop tops using profiles of highly ionized spectral lines of Fe XXIV and Fe XXIII formed at multimillion-degree temperatures. Non-thermal motions that may be due to turbulence or multiple flow regions along the line of sight are extracted from the line profiles. The non-thermal motions are measured for four flares seen at or close to the solar limb. The profile data are obtained using the Extreme-ultraviolet Imaging Spectrometer on the Hinode spacecraft. The multimillion-degree non-thermal motions are between 20 and 60 km s–1 and appear to increase with height above the loop tops. Motions determined from coronal lines (i.e., lines formed at about 1.5 MK) tend to be smaller. The multimillion-degree temperatures in the loop tops and above range from about 11 MK to 15 MK and also tend to increase with height above the bright X-ray-emitting loop tops. The non-thermal motions measured along the line of sight, as well as their apparent increase with height, are supported by Solar Dynamics Observatory Atmospheric Imaging Assembly measurements of turbulent velocities in the plane of the sky.

ON THE OBSERVABILITY OF OPTICALLY THIN CORONAL HYPERFINE STRUCTURE LINES

We present Cloudy calculations for the intensity of coronal hyperfine lines in various environments. We model indirect collisional and radiative transitions, and quantify the collisionally-excited line emissivity in the density-temperature phase-space. As an observational aid, we also express the emissivity in units of the continuum in the 0.4--0.7 keV band. For most hyperfine lines, knowledge of the X-ray surface brightness and the plasma temperature is sufficient for rough estimates. We find that the radiation fields of both Perseus A and Virgo A can enhance the populations of highly ionized species within 1 kpc. They can also enhance line emissivity within the cluster core. This could have implications for the interpretation of spectra around bright AGN. We find the intensity of the $^{57}$Fe XXIV {\lambda}3.068 mm to be about two orders of magnitude fainter than previously thought, at about 20 {\mu}K. Comparably bright lines may be found in the infrared. Finally, we find the intensity of hyperfine lines in the Extended Orion Nebula to be low, due to the shallow sightline. Observations of coronal hyperfine lines will likely be feasible with the next generation of radio and sub-mm telescopes.

SLIPPING MAGNETIC RECONNECTION DURING AN X-CLASS SOLAR FLARE OBSERVED BYSDO/AIA

We present SDO/AIA observations of an eruptive X-class flare of July 12, 2012, and compare its evolution with the predictions of a 3D numerical simulation. We focus on the dynamics of flare loops that are seen to undergo slipping reconnection during the flare. In the AIA 131A observations, lower parts of 10 MK flare loops exhibit an apparent motion with velocities of several tens of km/s along the developing flare ribbons. In the early stages of the flare, flare ribbons consist of compact, localized bright transition-region emission from the footpoints of the flare loops. A DEM analysis shows that the flare loops have temperatures up to the formation of Fe XXIV. A series of very long, S-shaped loops erupt, leading to a CME observed by STEREO. The observed dynamics are compared with the evolution of magnetic structures in the "standard solar flare model in 3D". This model matches the observations well, reproducing both the apparently slipping flare loops, S-shaped erupting loops, and the evolution of flare ribbons. All of these processes are explained via 3D reconnection mechanisms resulting from the expansion of a torus-unstable flux rope. The AIA observations and the numerical model are complemented by radio observations showing a noise storm in the metric range. Dm-drifting pulsation structures occurring during the eruption indicate plasmoid ejection and enhancement of reconnection rate. The bursty nature of radio emission shows that the slipping reconnection is still intermittent, although it is observed to persist for more than an hour.

EXTREME ULTRAVIOLET SPECTRA OF SOLAR FLARES FROM THE EXTREME ULTRAVIOLET SPECTROHELIOGRAPH SPIRIT ONBOARD THE CORONAS-F SATELLITE

We present detailed EUV spectra of 4 large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176-207 \AA\ and 280-330 \AA. These spectra were obtained {by the slitless} spectroheliograph SPIRIT aboard the CORONAS-F satellite. To our knowledge these are the first detailed EUV spectra of large flares obtained with spectral resolution of $\sim 0.1$ \AA. We performed a comprehensive analysis of the obtained spectra and provide identification of the observed spectral lines. The identification was performed based {on the calculation} of synthetic spectra (CHIANTI database was used), with simultaneous {calculations of DEM} and density of the emitting plasma. More than 50 intense lines are present in the spectra that correspond to a temperature range of $T=0.5-16$ MK; most of the lines belong to Fe, Ni, Ca, Mg, Si ions. In all the considered flares intense hot lines from Ca XVII, Ca XVIII, Fe XX, Fe XXII, and Fe XXIV are observed. The calculated DEMs have a peak at $T \sim 10$ MK. The densities were determined using Fe XI - Fe XIII lines and averaged $6.5 \times 10^9$ cm$^{-3}$. We also discuss the identification, accuracy and major discrepancies of the spectral line intensity prediction.

A revised radiometric calibration for the Hinode/EIS instrument

A preliminary assessment of the in-flight radiometric calibration of the Hinode EUV Imaging Spectrometer (EIS) is presented. This is done with the line ratio technique applied to a wide range of observations of the quiet Sun, active regions and flares from 2006 until 2012. The best diagnostic lines and the relevant atomic data are discussed in detail. Radiances over the quiet Sun are also considered, with comparisons with previous measurements. Some departures in the shapes of the ground calibration responsivities are found at the start of the mission. These shapes do not change significantly over time, with the exception of the shorter wavelengths of the EIS short-wavelength (SW) channel, which shows some degradation. The sensitivity of the SW channel at longer wavelengths does not show significant degradation, while that of the long-wavelength (LW) channel shows a significant degradation with time. By the beginning of 2010 the responsivity of the LW channel was already a factor of two or more lower than the values measured on the ground. A first-order correction is proposed. With this correction, the main ratios of lines in the two channels become constant to within a relative 20%, and the He II 256 A radiances over the quiet Sun also become constant over time. This correction removes long-standing discrepancies for a number of lines and ions, in particular those involving the strongest Fe X, Fe XIII, Fe XIV, Fe XVII, and Fe XXIV lines, where discrepancies of factors of more than two were found. These results have important implications for various EIS science analyses, in particular for measurements of temperatures, emission measures and elemental abundances.

Soft X-ray Fluxes of Major Flares Far Behind the Limb as Estimated Using STEREO EUV Images

With increasing solar activity since 2010, many flares from the backside of the Sun have been observed by the Extreme Ultraviolet Imager (EUVI) on either of the twin STEREO spacecraft. Our objective is to estimate their X-ray peak fluxes from EUVI data by finding a relation of the EUVI with GOES X-ray fluxes. Because of the presence of the Fe xxiv line at 192 A, the response of the EUVI 195 A channel has a secondary broad peak around 15 MK, and its fluxes closely trace X-ray fluxes during the rise phase of flares. If the flare plasma is isothermal, the EUVI flux should be directly proportional to the GOES flux. In reality, the multithermal nature of the flare and other factors complicate the estimation of the X-ray fluxes from EUVI observations. We discuss the uncer- tainties, by comparing GOES fluxes with the high cadence EUV data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We conclude that the EUVI 195 A data can provide estimates of the X-ray peak fluxes of intense flares (e.g., above M4 in the GOES scale) with uncertainties of a factor of a few. Lastly we show examples of intense flares from regions far behind the limb, some of which show eruptive signatures in AIA images.

CHROMOSPHERIC EVAPORATION IN AN M1.8 FLARE OBSERVED BY THE EXTREME-ULTRAVIOLET IMAGING SPECTROMETER ONHINODE

We discuss observations of chromospheric evaporation for a complex flare that occurred on 9 March 2012 near 03:30 UT obtained from the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. This was a multiple event with a strong energy input that reached the M1.8 class when observed by EIS. EIS obtained a full-CCD spectrum of the flare. Chromospheric evaporation characterized by 150-200 km/s upflows was observed in multiple locations in multi-million degree spectral lines of flare ions such as Fe XXII, Fe XXIII, and Fe XXIV, with simultaneous 20-60 km/s upflows in million degree coronal lines from ions such as Fe XII - Fe XVI. The behavior of cooler, transition region ions such as O VI, Fe VIII, He II, and Fe X is more complex, but upflows were also observed in Fe VIII and Fe X lines. At a point close to strong energy input in space and time, the flare ions Fe XXII, Fe XXIII, and Fe XXIV reveal an isothermal source with a temperature close to 14 MK and no strong blueshifted components. At this location there is a strong downflow in cooler active region lines from ions such as Fe XIII and Fe XIV. We speculate that this downflow may be evidence of the downward shock produced by reconnection in the current sheet seen in MHD simulations. A sunquake also occurred near this location.

PROPERTIES OF A SOLAR FLARE KERNEL OBSERVED BYHINODEANDSDO

Flare kernels are compact features located in the solar chromosphere that are the sites of rapid heating and plasma upflow during the rise phase of flares. An example is presented from a M1.1 class flare observed on 2011 February 16 07:44 UT for which the location of the upflow region seen by EIS can be precisely aligned to high spatial resolution images obtained by the Atmospheric Imaging Assembly (AIA) and Heliospheric Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). A string of bright flare kernels is found to be aligned with a ridge of strong magnetic field, and one kernel site is highlighted for which an upflow speed of 400 km/s is measured in lines formed at 10-30 MK. The line-of-sight magnetic field strength at this location is 1000 G. Emission over a continuous range of temperatures down to the chromosphere is found, and the kernels have a similar morphology at all temperatures and are spatially coincident with sizes at the resolution limit of the AIA instrument (< 400 km). For temperatures of 0.3-3.0 MK the EIS emission lines show multiple velocity components, with the dominant component becoming more blue-shifted with temperature from a redshift of 35 km/s at 0.3 MK to a blueshift of 60 km/s at 3.0 MK. Emission lines from 1.5-3.0 MK show a weak redshifted component at around 60-70 km/s implying multi-directional flows at the kernel site. Significant non-thermal broadening corresponding to velocities of 120 km/s is found at 10-30MK, and the electron density in the kernel, measured at 2 MK, is 3.4 x 10^10 cm-3. Finally, the Fe XXIV 192.03/255.11 ratio suggests that the EIS calibration has changed since launch, with the long wavelength channel less sensitive than the short wavelength channel by around a factor two.

Radiative cooling in collisionally ionized and photoionized plasmas

We discuss recent improvements in the calculation of the radiative cooling in both collisionally and photo ionized plasmas. We are extending the spectral simulation code Cloudy so that as much as possible of the underlying atomic data is taken from external databases, some created by others, some developed by the Cloudy team. This paper focuses on recent changes in the treatment of many stages of ionization of iron, and discusses its extensions to other elements. The H-like and He-like ions are treated in the iso-electronic approach described previously. Fe II is a special case treated with a large model atom. Here we focus on Fe III through Fe XXIV, ions which are important contributors to the radiative cooling of hot, 1e5 to 1e7 K, plasmas and for X-ray spectroscopy. We use the Chianti atomic database to greatly expand the number of transitions in the cooling function. Chianti only includes lines that have atomic data computed by sophisticated methods. This limits the line list to lower excitation, longer wavelength, transitions. We had previously included lines from the Opacity Project database, which tends to include higher energy, shorter wavelength, transitions. These were combined with various forms of the g-bar approximation, a highly approximate method of estimating collision rates. For several iron ions the two databases are almost entirely complementary. We adopt a hybrid approach in which we use Chianti where possible, supplemented by lines from the Opacity Project for shorter wavelength transitions. The total cooling including the lightest thirty elements differs significantly from some previous calculations.

Atomic data for transitions in Ar XVI and FeXXIV

Energy levels and radiative rates for E1, E2, M1, and M2 transitions among the lowest 24 levels, belonging to the n ≤ 5 configurations of Ar XVI and Fe XXIV, are calculated using the GRASP code. Collision strengths are also calculated over a wide energy range using the fully relativistic DARC code. Resonances are resolved in a fine energy mesh in the thresholds region and effective collision strengths are calculated for all 276 transitions at temperatures up to 107.7 K. Comparisons are made with the earlier available as well as other parallel calculations from the FAC code, and discrepancies are noted for some of the transitions in both ions.

PLASMA MOTIONS AND HEATING BY MAGNETIC RECONNECTION IN A 2007 MAY 19 FLARE

Based on scanning spectroscopic observations with the Hinode EUV imaging spectrometer, we have found a loop-top hot source, a fast jet nearby, and an inflow structure flowing to the hot source that appeared in the impulsive phase of a long-duration flare at the disk center on 2007 May 19. The hot source observed in Fe XXIII and Fe XXIV emission lines has the electron temperature of 12 MK and density of 1 Multiplication-Sign 10{sup 10} cm{sup -3}. It shows excess line broadening, which exceeds the thermal Doppler width by {approx}100 km s{sup -1}, with a weak redshift of {approx}30 km s{sup -1}. We have also observed a blueshifted faint jet whose Doppler velocity exceeds 200 km s{sup -1} with an electron temperature of 9 MK. Coronal plasmas with electron temperature of 1.2 MK and density of 2.5 Multiplication-Sign 10{sup 9} cm{sup -3} that flow into the loop-top region with a Doppler velocity of 20 km s{sup -1} have been identified in the Fe XII observation. They disappeared near the hot source, possibly by being heated to the hotter faint jet temperature. From the geometrical relationships of these phenomena, we conclude that they provide evidence for magnetic reconnection that occurs nearmore » the loop-top region. The estimated reconnection rate is 0.05-0.1, which supports the Petschek-type magnetic reconnection. Further supporting evidence for the presence of the slow-mode and fast-mode MHD shocks in the reconnection geometry is given based on the observed quantities.« less

The EVE Doppler Sensitivity and Flare Observations

The Extreme-ultraviolet Variability Experiment (EVE; see Woods et al., 2009) obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity of the EVE data. We find that the 30.4 nm line of He ii has a random Doppler error below 0.001 nm (1 pm, better than 10 km s−1 as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE’s optical layout, which (as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we find the line centroid to have a redshift of 16.8 ± 5.9 km s−1 relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as Fe xxiv 19.2 nm, have well-determined Doppler components for major flares, with decreasing apparent blueshifts as expected from chromospheric evaporation flows.

X-ray spectral measurements and collisional radiative modeling of laser produced iron plasma

Spatially-resolved time-integrated X-ray spectra of laser produced iron plasma were recorded, in the spectral range from 10 to 12 Å. The newest version of the atomic code HULLAC was used alongside a radiation-hydrodynamics code to model the plasma and generate simulated spectra for comparison with the experimental one. The spectra were found to be characterized by line emission from Li-like Fe XXIV ions, with 2s-3p and 2p-3d dominant transitions. Ionization stage, electron temperature and density were inferred from spectroscopic measurements. Good agreement was found between the parameters obtained from the radiation-hydrodynamics code and the detailed atomic code.