ФИАН
Научная деятельность
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Публикации
2016
- A. Reva, A. Ulyanov, S. Shestov, S. Kuzin
BREAKOUT RECONNECTION OBSERVED BY THE TESIS EUV TELESCOPE 1 международная конференция 'Прикладная оптика-2004'. Сборник трудов. Т.2. Оптические технологии и материалы., vol. 816, N2, pp. 90, (2016)
аннотация
We present experimental evidence of the coronal mass ejection (CME) breakout reconnection, observed by the TESIS EUV telescope. The telescope could observe solar corona up to 2 R⊙ from the Sun center in the Fe 171 Å line. Starting from 2009 April 8, TESIS observed an active region (AR) that had a quadrupolar structure with an X-point 0.5 R⊙ above photosphere. A magnetic field reconstructed from the Michelson Doppler Imager data also has a multipolar structure with an X-point above the AR. At 21:45 UT on April 9, the loops near the X-point started to move away from each other with a velocity of 7 km s−1. At 01:15 UT on April 10, a bright stripe appeared between the loops, and the flux in the GOES 0.5–4 Å channel increased. We interpret the loops\\\' sideways motion and the bright stripe as evidence of the breakout reconnection. At 01:45 UT, the loops below the X-point started to slowly move up. At 15:10 UT, the CME started to accelerate impulsively, while at the same time a flare arcade formed below the CME. After 15:50 UT, the CME moved with constant velocity. The CME evolution precisely followed the breakout model scenario.
2015
- Shestov S., Nakariakov V. M., Kuzin S.
Fast Magnetoacoustic wave trains of sausage symmetru in cylindrical waveguides of the solar corona 1 международная конференция 'Прикладная оптика-2004'. Сборник трудов. Т.2. Оптические технологии и материалы., vol. 814, N2, pp. 135, (2015)
аннотация
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.
- A. Reva, S. Shestov, I. Zimovets, S. Bogachev, S. Kuzin
Wave-like formation of Hot Loop Arcades 1 международная конференция 'Прикладная оптика-2004'. Сборник трудов. Т.2. Оптические технологии и материалы., vol. 290, N10, pp. 2909, (2015)
аннотация
We present observations of hot arcades made with the Mg XII spectroheliograph onboard the CORONAS-F mission, which provides monochromatic images of hot plasma in the Mg XII 8.42 Å resonance line. The arcades were observed to form above the polarity inversion line between active regions NOAA 09847 and 09848 at four successive episodes: at 09:18, 14:13, and 22:28 UT on 28 February 2002, and at 00:40 UT on 1March 2002. The evolution of the arcades can be described as: a) a small flare (precursor) appeared near the edge of the still invisible arcade, b) the arcade brightened in a wave-like manner – closer
loops brightened earlier, and c) the arcade intensity gradually decreased in 1 h. The esti- mated wave speed was 700 kms−1, and the distance between the hot loops was 50 Mm. The arcades formed without visible changes in their magnetic structure. The arcades were
probably heated up by the instabilities of the current sheet above the arcade, which were caused by a magnetohydrodynamic wave excited by the precursor
2014
- Reva, A Shestov, S Bogachev, S Kuzin, S
Extreme Ultraviolet Spectra of Solar Flares From the Extreme Ultraviolet Spectroheliograph Spirit Onboard the Coronas-F Satellite Tech. Phys, vol. 780, pp. 15, (2014)
аннотация
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 Å and 280-330 Å. 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 Å. 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.
2012
- Reva, A Shestov, S Bogachev, S Kuzin, S
Investigation of Hot X-Ray Points (HXPs) Using Spectroheliograph Mg xii Experiment Data from CORONAS-F/SPIRIT 1 международная конференция 'Прикладная оптика-2004'. Сборник трудов. Т.2. Оптические технологии и материалы., vol. 276, pp. 97-112, (2012)
аннотация
Observations in the Mg XII 8.42 Å line onboard the CORONAS-F satellite have revealed compact high temperature objects – hot X-ray points (HXPs) – and their major physical parameters were investigated. Time dependencies of temperature, emission mea- sure, intensity, and electron density were measured for 169 HXPs. HXPs can be divided into two groups by their temperature variations: those with gradually decreasing temperature and those with rapidly decreasing temperature. HXP plasma temperatures lie in the range of 5 – 40 MK, the emission measure is 10^45 –10^48 cm−3, and the electron density is above 1010 cm−3, which exceeds the electron density in the quiet Sun (10^8 –10^9 cm−3). HXP life- times vary between 5 – 100 minutes, significantly longer than the conductive cooling time. This means that throughout a HXP’s lifetime, the energy release process continues, which helps to maintain its high temperature. A HXP’s thermal energy is not greater than 1028 erg, and the total energy which is released in HXPs does not exceed 10^30 erg. HXPs differ in their physical properties from other flare-likemicroevents, such asmicroflares, X-ray bright points, and nanoflare
2007
- S.V.Kuzin, S.A. Bogachev, I.A. Zhitnik, A.A. Pertsov , A.P. Ignat'ev, A.V. Mitrofanov, V.A. Slemzin, S.V. Shestov, N.K. Suhodrev, O.I. Bugaenko,
The TESIS experiment on EUV imaging spectroscopy of the Sun Advances in Space Research, (2007)
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