S. V. Shestov

The TESIS experiment on the CORONAS-PHOTON spacecraft

On February 26, 2009, the first data was obtained in the TESIS experiment on the research of the solar corona using imaging spectroscopy. The TESIS is a part of the scientific equipment of the CORONAS-PHO-TON spacecraft and is designed for imaging the solar corona in soft X-ray and extreme ultraviolet regions of the spectrum with high spatial, spectral, and temporal resolutions at altitudes from the transition region to three solar radii. The article describes the main characteristics of the instrumentation, management features, and operation modes.

Solar plasma temperature diagnostics in flares and active regions from spectral lines in the range 280–330 Å in the SPIRIT/CORONAS-F experiment

Plasma temperature diagnostics in solar flares and active regions has been carried out using data from the SPIRIT spectroheliograph onboard the CORONAS-F satellite. The temperature distribution of the differential emission measure (DEM) has been determined from the relative intensities of spectral lines recorded in the spectral range 280–330 Å in the period from 2001 to 2005. Analysis of these distributions has led to the conclusion about the existence of active regions with various “characteristic” temperature compositions. The presence of a hot plasma with temperatures logT = 6.8−7.2 in active regions has been established for the first time from XUV spectroscopic data and monochromatic X-ray line images. The DEM distribution for intense long-decay flares has also been obtained for the first time and a similarity of the temperature compositions for flares of different classes at the decay phase has been found. The spectra have been modeled on the basis of the calculated DEMs. The systematic discrepancies between the calculated and measured line intensities are discussed.

Advanced materials for multilayer mirrors for extreme ultraviolet solar astronomy

We provide an analysis of contemporary multilayer optics for extreme ultraviolet (EUV) solar astronomy in the wavelength ranges: λ=12.9-13.3  nm, λ=17-21  nm, λ=28-33  nm, and λ=58.4  nm. We found new material pairs, which will make new spaceborne experiments possible due to the high reflection efficiencies, spectral resolution, and long-term stabilities of the proposed multilayer coatings. In the spectral range λ=13  nm, Mo/Be multilayer mirrors were shown to demonstrate a better ratio of reflection efficiency and spectral resolution compared with the commonly used Mo/Si. In the spectral range λ=17-21  nm, a new multilayer structure Al/Si was proposed, which had higher spectral resolution along with comparable reflection efficiency compared with the commonly used Al/Zr multilayer structures. In the spectral range λ=30  nm, the Si/B4C/Mg/Cr multilayer structure turned out to best obey reflection efficiency and long-term stability. The B4C and Cr layers prevented mutual diffusion of the Si and Mg layers. For the spectral range λ=58  nm, a new multilayer Mo/Mg-based structure was developed; its reflection efficiency and long-term stability have been analyzed. We also investigated intrinsic stresses inherent for most of the multilayer structures and proposed possibilities for stress elimination.

On the spatial and temporal characteristics and formation mechanisms of soft X-ray emission in the solar corona

Our main goal is to show that the spatial and temporal dynamics of the temperature content for plasma structures in the solar corona can be described quantitatively in principle, which is necessary for understanding the formation mechanisms of soft X-ray emission. An approach based on a consistent modeling of complex data from the CORONAS-F, GOES, and RHESSI satellites is suggested. A basically new element of this approach is the use of time series of monochromatic full-Sun images in the X-ray MgXII 8.42 Å line and EUV lines obtained in the SPIRIT experiment onboard CORONAS-F. Two inversion procedures have been used to determine the volume and column differential emission measures defined by the Stieltjes integral: an optimization one based on a multitemperature parametric model and an iterative one based on the Bayesian theorem, respectively. The calculations with coronal abundances agree with the RHESSI data within the experimental error limits, while those with photospheric abundances give no satisfactory agreement. The relatively cold (with temperature 2–4 MK) and transient (4–10 MK) plasmas are shown to play a significant role in producing soft X-ray emission during flare events and in their energy budget. The spatial electron density and temperature distributions and their time evolution have been obtained for long-duration events that were first observed in the monochromatic MgXII channel and were previously called “spiders.” The method used has allowed us to verify the absolute intercalibration of the fluxes recorded in all experiments and to reference the SPIRIT MgXII images to the solar disk. We also consider possible flare plasma heating mechanisms for impulsive and long-duration (spider) flare events.

EUV observations of the solar corona with superhigh spatial resolution in the ARCA project

Observing the Sun’s hot corona with sub-second spatial resolution is important in solving a number of basic solar physics problems. The new ARCA satellite observatory under development at the Lebedev Physical Institute, Russian Academy of Sciences, will be first to provide images of the hot solar corona with a spatial resolution of about 0.18 arcsec. Scientific and technical features of the observatory are discussed.

Electron density diagnostics for various plasma structures of the solar corona based on Fe XI-FeXIII lines in the range 176–207 Å measured in the SPIRIT/CORONAS-F experiment

The relative intensities of FeXI-Fe XIII lines in the range 176–207 Å have been measured for various plasma structures of the solar corona using data from the XUV spectroheliograph of the SPIRIT instrumentation onboard the CORONAS-F satellite with an improved spectral sensitivity calibration. Electron density diagnostics of a plasma with temperatures 0.8–2.5 MK has been carried out in active regions, quiet-Sun and off-limb areas, and, for the first time, in extremely intense solar flares. The density range is (1.6–8) × 109 cm−3 for flares, (0.6–1.6) × 109 cm−3 for active regions, and ∼5 × 108 cm−3 for quiet-Sun areas. The calibration accuracy of the spectral sensitivity for the spectroheliograph has been analyzed based on spectral lines with density-independent intensity ratios.

Fast magnetoacoustic wave trains of sausage symmetry in cylindrical waveguides of the solar corona

Fast magnetoacoustic waves guided along the magnetic field by plasma non-uniformities, in particular coronal loops, fibrils and plumes, are known to be highly dispersive, which leads to the formation of quasi-periodic wave trains excited by a broadband impulsive driver, e.g. a solar flare. We investigated effects of cylindrical geometry on the fast sausage wave train formation. We performed magnetohydrodynamic numerical simulations of fast magnetoacoustic perturbations of a sausage symmetry, propagating from a localised impulsive source along a field-aligned plasma cylinder with a smooth radial profile of the fast speed. The wave trains are found to have pronounced period modulation, with the longer instant period seen in the beginning of the wave train. The wave trains have also a pronounced amplitude modulation. Wavelet spectra of the wave trains have characteristic tadpole features, with the broadband large-amplitude heads preceding low-amplitude quasi-monochromatic tails. The mean period of the wave train is about the transverse fast magnetoacoustic transit time across the cylinder. The mean parallel wavelength is about the diameter of the waveguiding plasma cylinder. Instant periods are longer than the sausage wave cutoff period. The wave train characteristics depend on the fast magnetoacoustic speed in both the internal and external media, and the smoothness of the transverse profile of the equilibrium quantities, and also the spatial size of the initial perturbation. If the initial perturbation is localised at the axis of the cylinder, the wave trains contain higher radial harmonics that have shorter periods.

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

We present detailed extreme ultraviolet (EUV) spectra of four large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176-207 A and 280-330 A. These spectra were obtained by the slitless spectroheliograph SPIRIT onboard the CORONAS-F satellite. To our knowledge, these are the first detailed EUV spectra of large flares obtained with a spectral resolution of ~0.1 A. 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 (the CHIANTI database was used), with simultaneous calculations of the differential emission measure (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, and 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 ~ 10 MK. The densities were determined using Fe XI-Fe XIII lines and averaged 6.5 × 109 cm–3. We also discuss the identification, accuracy, and major discrepancies of the spectral line intensity prediction.

X-ray and EUV diagnostics of active plasma structures with the RES spectroheliograph in the SPIRIT experiment onboard the CORONAS-F satellite

We provide a brief overview of the main methods and results of spectroscopic studies of several active plasma structures in the solar corona with the RES spectroheliograph in the SPIRIT experiment. This instrument has allowed ∼ 150 monochromatic images of the entire Sun in extreme UV (EUV) lines in the 175-to 205-and 280-to 330-Å spectral bands and in the X-ray Mg XII 8.42-Å line to be simultaneously obtained for the first time. The RES instrument has taken ∼ 300000 spectroheliograms with a high time resolution over the period of its operation since the launch of the satellite on July 31, 2001. The accumulated data were used to construct and calibrate the spectra of solar flares and compact active regions with a spectral resolution of 0.04 Å. Based on EUV spectra, we determined the temperature distributions of the electron density and differential emission measure (DEM) for several active plasma structures observed in the RES X-ray channel: active regions, flares, and spiders. The results of modeling the physical conditions in an emitting plasma were used to analyze the formation and dynamics of plasma structures detected in the monochromatic X-ray images of the entire Sun.

Complex of instrumentation KORTES for the EUV and x-ray imaging and spectroscopy of the solar corona

We report on the current status of the KORTES project – the first sun-oriented mission for the International Space Station to be launched in 2016-2017. KORTES will comprise several imaging and spectroscopic instruments that will observe solar corona in a number of wavebands, covering EUV and X-Ray ranges. A brief overview of the instrumentation of KORTES, its’ layout, technical parameters and scientific objectives is given. An additional attention is given to the design of multilayer optics and filters to be employed in EUV instruments of KORTES.