Soft X-ray oscillations from AT Mic: Flare plasma diagnostics

We consider the flare oscillations from the active red dwarf AT Mic detected with the XMM-Newton space observatory in the soft X-ray energy range (0.2–12 keV). Following Mitra-Kraev et al. (2005a), we associate the observed oscillations with a period of ≈750 s with the excitation of a standing slow magnetoacoustic (SMA) wave in a coronal loop. The damping of flare loop SMA oscillations is shown to be governed by electron thermal conduction. We have estimated the plasma density (≈3 × 10¹⁰ cm^?3) and the minimum magnetic field strength (≈100 G) in the region of flare energy release. The adopted model is consistent with the results of a spectral analysis of the soft X-ray emission. The piston mechanism is assumed to be responsible for the excitation of loop SMA oscillations.     

Long-lived hot coronal structures observed with CORONAS-F/SPIRIT in the Mg XII line

Large-scale hot features were detected and observed several times high in the solar corona in the high-temperature Mg XII line (T = 5–20 MK, T _max = 10 MK) with the soft X-ray telescope of the SPIRIT instrumentation complex onboard the CORONAS-F spacecraft. These features look like a spider up to 300000 km in size and live up to a few days. Their bright cores observed at heights were from 0.1 to 0.3 solar radii are connected with active regions by darker legs, giant loops. These features are disposed above arcades, which are simultaneously observed in cooler emission lines sensitive to temperatures of 1 to 2 MK. For the core of such a feature observed December 28–29, 2001, Zhitnik et al. (2003a) estimated an electron temperature of 10 MK and a number density of n _e ≈ 10¹⁰ cm^?3. A high activity and an association with eruptive phenomena were found for such features in continuous (up to 20-day) observations with a cadence of 0.6–1.7 min. In the present paper, we discuss the relation of such features to coronal structures, which are known from previous studies. We identify such off-limb features observed with SPIRIT on October 22, November 12, and December 28–29, 2001, with hot upper parts of post-eruptive arcades. The results of multifrequency analysis of these features based on the data obtained in various spectral ranges by different instruments (Yohkoh/SXT, SOHO/EIT, SOHO/LASCO, Nobeyama and SSRT radioheliographs) are briefly discussed. We address the physical conditions of the long-term existence of giant hot coronal structures. It is demonstrated that the post-eruptive energy release must be prolonged and the condition β ? 1 is not satisfied in these structures. It is argued that the so-called “standard flare model” should be better considered as a “standard post-eruptive energy release model.”     

Type-II Spicules as Important Sources of Both Heating and Sustain the Mass Loss of Solar Corona

Geomagnetism and Aeronomy - Heat fluxes from hot open magnetic flux tubes into the surrounding corona as a possible source of corona heating are determined. In order to compensate for radiation and...     

Linear weathering crusts in the upper Amur region

The upper Amur region comprises weathering crusts (waste mantle developed at copper-nickel sulfide deposits included), which appreciably hamper the prospecting for such deposits. In order to develop their prospecting criteria, the composition of linear weathering crusts above a nickeliferous cortlandite dike and barren pyroxenite dike, as well as in the fracture zone above metamorphic rocks, was investigated. The chemical composition of material in the weathering crust and the mineral composition of newly formed clay fractions and heavy concentrate were determined. It was established that weathering crust in the nickeliferous cortlandite dike is characterized by the prevalence of fine jarosite fraction with crystobalite admixture. The heavy concentrate samples contain jarosite along with a small amount of relict sulfides (pyrite and galena) and native gold. These criteria can be used in the prospecting for copper-nickel sulfide mineralization in the upper Amur region and other similar regions.     

Structural features of the subauroral ionosphere during the origination of the polarization jet

Narrow jets of rapid westward ion drifts were registered near the plasmapause projection at the F-region altitudes on the Cosmoc-184 satellite and were called “a polarization jet.” In this work, the effect of this polarization jet on the ionospheric structure has been studied, using a three-dimensional model of the high-latitude ionosphere, when strong local magnetospheric electric fields were originated. The calculations indicated that a narrow trough in the latitudinal variations in the electron density at the F-region maximum was formed in the zone where the electric field was switched on. This trough was more pronounced in the early evening hours, when the electron background density was still high, and was less distinct at low back-ground levels during premidnight hours. A comparison of the calculations and experimental data indicated that they were in good agreement with one another, which made it possible to state that the polarization jet was the main mechanism by which narrow electron density troughs were formed in the subauroral ionosphere.     

Pulsations of non-thermal emissions from the solar flare of November 5, 1992 and the trap-plus-precipitation model

The fine structure of the time variations of microwave and hard X-ray emissions from the solar flare of November 5, 1992 was analyzed. On the basis of the wavelet analysis, pulsations of intensity with a period of about 6 s were revealed in both the data sets. The observed time delay between the coronal plasma emission measure maximum and the temperature maximum is consistent with the concept of chromospheric evaporation. The anticorrelation observed between the time profiles of the microwave and hard X-ray emissions and the nature of the time delays between the peaks are associated with the excitation of radial fast magneto-acoustic oscillations in the flare loop (a coronal trap). Consequences of the obtained results are discussed.     

Ballooning Instability in Coronal Flare Loops

Within the framework of ideal magnetohydrodynamics the excitation of the ballooning instability in a toroidal coronal loop with a radius of cross section a and a radius of curvature R is analyzed by using the energy method. Kink oscillations are able to excite the ballooning instability when the plasma beta parameter β>2a/R. It has been suggested that this can result in the formation of cusp-shaped coronal loops. Modulation of gyrosynchrotron emission caused by kink oscillations is considered. The intensity of gyrosynchrotron emission for optically thin sources is the most sensitive to Alfvén disturbances. The obtained theoretical results are discussed in the light of Yohkoh, SOHO, TRACE, RHESSI, and Nobeyama observations.