[en] Radio observations explain certain kinds of stellar activity and reliable estimates of magnetic field strengths are derived for the radio emitting regions. Radio observation of flare stars shows rapidly varying bursts of radiation with frequencies of up to 5 GHz. The inferred brightness temperatures of these bursts (10 to the 10th power to 10 to the 14th power) imply that the radiation is coherent. Two mechanisms are proposed to generate such radiation: (1) plasma radiation, and (2) electron cyclotron masers. The high brightness temperatures of the bursts up to 10 to the 20th power K) makes the latter the most plausible. For bursts in the 5 GHz range, the magnetic field strength would be approximately 900 Gauss

[en] The nature of the peculiar emission properties of the T Tauri stars is examined in the light of contributions from regions designated as photospheres, chromospheres coronae, and extended envelopes which are often characterized by mass loss. Although some manifestations of T Tauri activity can be linked to vigorous solar-stellar phenomena characteristic of cool stars of low mass, other characteristics of T Tauri behavior exhibited by a wide range of young stellar objects

No abstract available

[en] Using analytical methods, the authors study the reasons for the formation of a magnetic-surface island structure in the central region of l=3 stellarator and torsatron magnetic configurations. Possible methods of substantially reducing the dimensions of this structure at minimum magnetic-configuration distortions are discussed. Magnetic configurations are considered both in vacuum and in the presence of a plasma. (author)

[en] In order to test the plasma wall interaction in a stellarator machine, the project Wendelstein7-X is in the beginning of the building up phase. As thermally highest loaded part of the machine, the target plates of the of the divertor will be exposed to maximum heat loads of 10 MW/m² up to 1000 s. Due to safety reasons the target elements should sustain heat loads up to 12 MW/m² and short time failure loads of 15 MW/m² without damage. The position of the cryopumps behind the target plates will lead to special elements including a cooling flow reversal element. Under this boundary conditions an alternative concept of target elements has been developed, analyzed and tested. Thermomechanical analyzes at 10 MW/m² using the method of Finite Elements are performed to select the optimum cross-section geometry and a proper material combination. Due to the lowest surface temperature of 830 C, the lowest peaking factor and the lowest residual stresses in the carbon fiber-reinforced carbon (CFC-material), the monoblock concept using the CFC material DMS704 or N11 brazed onto two parallel copper tubes of 26 mm distance is chosen as best solution for the realization of the target elements. The bonding of the copper tubes with the CFC will be done by active brazing with a partial liquid phase. The liquid brase phase is formed by the interaction of a deposited thin layer of titanium with the surface of the copper tubes. Heat load experiments in the electron beam facility TSEFEY and the ion beam facility MARION, nondestructive and metallographic inspections show that the main reason for defects in the braze interface are due to a lack of liquid phase. In order to avoid these defects, the braze gap at room temperature must be adjusted as small as possible. In addition a large amount of braze depots are placed on the rear side of the target elements to overcome the problem of manufacturing tolerances. One target element, manufactured under these conditions, is successfully tested up to power densities of 10.5 MW/m², using a coolant flow velocity of 10 m/s. At higher power densities a failure of the cooling is observed and large cracks occur in the CFC material parallel to the fiber planes. (orig.)

[en] The dMe flare star UV Ceti (L726-8B) was observed at four frequencies simultaneously in the 1385-1652 MHz band using the Very Large Array. A flare lasting 10 minutes was observed with 6.67 s time resolution 'Dynamic spectrum'-type images in the Stokes parameters I and V show considerable complexity in the frequency-time domain; some features show a positive frequency drift with time, while others are more complex, involving both positive and negative frequency drifts. The positive drift features would be consistent with disturbances traveling downward in the star's corona. 13 references

No abstract available

[en] We consider the structure of a particular class of 2D x-invariant magnetostatic equilibria in which the magnetic field is potential everywhere in some domain of space but on some singular surfaces - current-sheets - carrying a non-zero net x-current. We establish some new general properties of configurations of this type, and discuss a variational principle allowing to compute them

[en] This paper is a review of the progress mode in understanding the stellar activity in the last decade, a summary of the important results from all this work and a description of some of the current exciting work underway in this field

[en] This paper summarizes the fluctuation theory of stellar mass loss which attempts to describe mass loss in terms of statistics. (Auth.)