We describe the RESIK (REntgenovsky Spektrometr s Izognutymi Kristalami) instrument, consisting of two double-channel X-ray spectrometers, designed to observe solar active region and flare plasmas. RESIK is one of the instruments making up the scientific payload of the Russian CORONAS-F solar mission. The uncollimated spectrometer uses two silicon and two quartz bent crystals observing flare, active region and coronal spectra in four wavelength bands with a resolving power (λ/ λ) of ∼1000. The wavelength coverage, 3.3 -6.1Å, includes emission lines of Si, S, Cl, Ar, and K and in the third diffraction order, the wavelength range includes He-like Fe lines (1.85Å) and Ni lines (1.55Å) with dielectronic satellites, emitted during intense, hot flares. The instrument is believed to be the best calibrated space-borne crystal spectrometer flown to date. The spectrometer dynamically adjusts the data gathering intervals from 1 s to 5 minutes, depending on the level of solar X-ray emission at the time of observation. The principal aims of RESIK are the measurements of relative and absolute element abundances in the emitting plasma and the temperature distribution of plasma (differential emission measure) over the temperature interval 3 and 50 MK. This paper summarizes the scientific objectives of RESIK and describes the design, characteristics, and performance of the instrument.
Aims. The Spectrometer Telescope for Imaging X-rays (STIX) on Solar Orbiter is a hard X-ray imaging spectrometer, which covers the energy range from 4 to 150 keV. STIX observes hard X-ray bremsstrahlung emissions from solar flares and therefore provides diagnostics of the hottest (⪆10 MK) flare plasma while quantifying the location, spectrum, and energy content of flare-accelerated nonthermal electrons. Methods. To accomplish this, STIX applies an indirect bigrid Fourier imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 coarsely pixelated CdTe detectors to provide information on angular scales from 7 to 180 arcsec with 1 keV energy resolution (at 6 keV). The imaging concept of STIX has intrinsically low telemetry and it is therefore well-suited to the limited resources available to the Solar Orbiter payload. To further reduce the downlinked data volume, STIX data are binned on board into 32 selectable energy bins and dynamically-adjusted time bins with a typical duration of 1 s during flares. Results. Through hard X-ray diagnostics, STIX provides critical information for understanding the acceleration of electrons at the Sun and their transport into interplanetary space and for determining the magnetic connection of Solar Orbiter back to the Sun. In this way, STIX serves to link Solar Orbiter’s remote and in-situ measurements.
The X-ray light curves in the 0.4È1.5 keV and 2È7 keV bands of the RS CVn binary AR Lacertae observed on 1993 June 1È3 over one full orbital cycle with the ASCA satellite have been used to map the spatial structure of AR LacÏs coronae. We Ðnd that both stars are X-ray active, that the corona of the K-type secondary star appears to be hotter than that of the G-type primary star, that X-ray emission is concentrated on the sides of the stars facing each other, and that there are compact and well-localized regions of enhanced X-ray emission with heights much smaller than the stellar radii. In one class of solutions there are additional extended regions with dimensions similar to or greater then the radii of the underlying stars which may be structures that interconnect the two stars. There are also other acceptable models without extended structures, however our analysis indicates that solutions with extended sources are more probable. Also, about 50% of the X-ray emission is unmodulated and could come from either an extended halo region, from the poles of the larger K star, or from other symmetric or uneclipsed structures in the orbital plane. We compare the coronal structures inferred from the ASCA observations with those inferred using the same technique from an EXOSAT observation of AR Lac made in 1984 and Ðnd that there are substantial di †erences between the coronal structures at these two epochs. For the solution with extended material in the orbital plane, we have derived the rough physical parameters for the X-rayÈemitting plasma, using the derived information on the spatial sizes of the various spatial components together with information about the emission measure and temperatures obtained from a simple spectral analysis of the ASCA data.
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