Analysis of the intensities and profiles of the spectral line Mg xii 8.42 Å in the solar X-ray spectrum

High resolution profiles of the Mg xii 8.42 Å line in the solar X-ray spectrum were recorded from the Intercosmos 7 satellite. The Mg xii line intensity provides a sensitive indicator of the hot plasma content (T ? 3 × 10⁶ K) in coronal condensations and X-ray flare volumes. The ratio of the line intensity to the intensity of the adjacent continuum has been used to compute approximate thermal models of the emitting regions. For all the investigated coronal condensations the temperature distribution of plasma has been found to be a function monotonically decreasing with temperature. But for some X-ray bursts there occurred a distinct excess of the hot plasma of temperature between 6–10 × 10⁶K. FWHM values of the Mg xii line profiles have been used to estimate ion temperature in the emitting regions.     

Extreme vacuum ultraviolet solar spectra obtained during the SPIRIT experiment aboard CORONAS-F: A catalog of lines in the range 280–330 Å

We present a catalog of 100 lines in the wavelength range 280–330 Å detected by the RES-C spectroheliograph in solar active regions and flares during the SPIRIT experiment aboard the CORONAS-F orbital station. We identified 54 lines. The line intensities recorded during the X3.4 (GOES) solar flare of December 28, 2001, are given. The data reduction procedure is discussed.     

Global Variations and Asymmetry of the Sun During Extremely High Activity in October–November 2003

The data of the Coronas F satellite and other spacecraft were used to show that, in October–November 2003, global variations in brightness occurred in all spectral regions of the solar electromagnetic radiation. The variations were asymmetric in heliolongitude. This phenomenon was accompanied by an extremely strong energy release in the form of coronal-mass ejections and solar flares. The most powerful of them took place on the solar side that was characterized by an enhanced brightness even before these events. As a result, superimposed corotating and sporadic disturbances, which are partly correlated, can be traced in parameters of the solar atmospheric radiation, flows of the solar-wind plasma, and heliospheric magnetic field.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 3, 2005, pp. 195–201.Original Russian Text Copyright © 2005 by Veselovsky, Dmitriev, Zhitnik, Zhukov, Zel’dovich, Kuzin, Naumkin, Persiantsev, Ryazanov, Shugai, Yakovchuk, Bogachev, Shestov.     

Solar flare X-ray spectra

Spectra of 3 large flares on 24 Oct., 5 Nov. and 16 Nov. 1970 in the region = 1.75–1.95 Å, obtained with the help of the Intercosmos-4 satellite during solar activity maximum are given. The physical conditions at the initial and final (decaying) phases are mainly studied. The line spectra are compared with hard continuum in the region 8–80 keV and results of polarization measurements, obtained simultaneously aboard the same satellite.     

Analysis of the high-resolution x-ray spectra obtained aboard the intercosmos 16 satellite

The Bragg-type, flat ADP crystal spectrometer, launched on board the INTERCOSMOS 16 satellite has been used for measurements of the X-ray spectra emitted from solar active region plasmas. During the period of the instrument operation (August–September, 1976) only a few active regions were present on the Sun (minimum of the solar activity). About 60 spectra have been registered. In the present paper using a spectrum averaged over 20 scans, we measured the wavelengths corresponding to the statistically significant spectral features seen in this spectrum in the wavelength range 9.14–9.33 Å. By comparison with the calculated line wavelengths and intensities predicted in the framework of the thermal model of the average active region, we performed the identification of these features. Besides rather prominent resonance, intercombination, and forbidden lines of the He-like ion Mg xi, it was possible to identify the satellite lines which correspond to 1s ² nl - 1s2p nl transitions from the states with n = 2, 3, and 4. The present paper is the first in a series dealing with the INTERCOSMOS 16 Mg xi spectra.     

Analysis of a solar eruptive event on November 4, 2001, using CORONAS-F/SPIRIT data

We analyze large-scale solar activity following the eruption of a very powerful, geoeffective coronal mass ejection in the 23rd solar cycle, observed at 175, 284, and 304 Å on November 4, 2001, using data from the CORONAS-F/SPIRIT telescope. In particular, we have shown that the restructuring of the magnetic field above the eruption center was accompanied by the formation of a multicomponent post-eruptive arcade, which was observed in all three bands over many hours and had an extent of the order of 0.5R_⊙. Two kinds of dimmings were observed, i.e., compact dimmings on either side of this arcade and channeled dimmings along some extended features beyond the active region. The intensity in the dimmings decreased by several tens of percent. The enhanced emission observed at the top of the post-eruptive arcade can be due to energy release in the course of magnetic reconnection high in the corona at the relaxation stage of the perturbed magnetic field to a new equilibrium state with a closed configuration. It can also be due to an enhanced emission measure because of the oblique direction of the line of sight crossing both loop tops and footpoint regions. The spatial coincidence of the main dimmings in lines corresponding to different temperatures indicates that a plasma outflow from the transition region and coronal structures with opened field lines are responsible for these dimmings. Variations in the plasma temperature associated with coronal mass ejections probably play an important role for some dimmings, which appear different in different lines.     

Quasi-periodicity of MgXII X-ray bursts revealed by CORONAS-F SPIRIT data for solar active regions

A spectral analysis of a series of integrated MgXII 8.42 Å X-ray intensities recorded by the CORONAS-F SPIRIT spectroheliometer is presented. Statistically significant peaks for periods in the intervals 12–30 min and 40–200 min were found in the power spectra. The power spectrum for these periods changed after the emergence of new photospheric magnetic flux in the active region NOAA 9840.     

Analysis of the high-resolution Mg XI X-ray spectra

In Part IV of the series of papers about the analysis of the INTERCOSMOS 16 ADP spectra a method is developed to evaluate plasma densities from measured resonance, intercombination, and forbidden helium-like Mg xi line intensities, using plots of the so-called G and R ratios. The density is close to the low-density limit. For the active region McMath 14352 a correlation between mean plasma density and electron temperature has been found, in agreement with earlier results. In an appendix systematic differences between measured and calculated line fluxes in all bands A to F are discussed.     

The Dynamics of High-Temperature Plasma in the Solar Corona according to SPIRIT Observations in Mg XII 8.42 Å Line

The spatial-distribution dynamics of the hot coronal plasma with T ～ 10 MK during a period of high solar activity is studied. We analyze images of the NOAA 9830 active region and its surroundings obtained during the second half of February 2002 with the SPIRIT spectroheliograph in the Mg XII 8.42-Å line and simultaneously on the SOHO satellite with the EIT instrument and on the TRACE satellite in the 195-Å channel. As shown by a multiwavelength analysis, a high-temperature plasma is concentrated in the corona near the apices of magnetic loops, it has long lifetimes (up to several days), and its dynamics is complex and bears no direct relation to flare activity. During the flares, conspicuous increases are observed in the X-ray flux and the emission measure for temperatures of ～5–15 MK. Our analyses of the time variations in emission during a flare suggest that hot plasma is heated by fluxes of accelerated electrons.     

Effects of the Absorption of Solar XUV Radiation by the Earth's Upper Atmosphere at Altitudes of 100–500 km in the X-ray Solar Images Obtained Onboard the Coronas-I (TEREK Telescope) and Coronas-F (SPIRIT X-ray Complex) Satellites

We consider the effects of the absorption of solar XUV radiation by the Earth's atmosphere that were observed in the solar images obtained with the TEREK-K telescope onboard the Coronas-I satellite in May–June 1994 at low solar activity and with the SPIRIT instrumentation onboard the Coronas-F satellite in October–November 2001 at maximum solar activity. The solar images were recorded during the satellite occultation: in the 175- and 304-A spectral ranges onboard Coronas-I with the TEREK-K telescope and in the 175-, 304-, and 8.42-A ranges onboard Coronas-F with the SPIRIT instrumentation. Based on the XUV solar images obtained during atmospheric sounding, apart from the total absorption, we can determine the direction of the atmospheric density gradient and study the local absorption variations with altitude on spatial scales of less than 1 km. The described method can significantly supplement the data obtained in studies of the upper atmosphere by the methods of mass spectrometry, incoherent radar scattering, and the drag of orbital spacecraft.