Spots structure and stratification of helium and silicon in the atmosphere of He-weak star HD 21699

The magnetic star HD 21699 possesses a unique magnetic field structure where the magnetic dipole is displaced from the centre by 0.4 +/- 0.1 of the stellar radius (perpendicularly to the magnetic axis), as a result, the magnetic poles are situated close to one another on the stellar surface with an angular separation of 55$^o$ and not 180$^o$ as seen in the case of a centred dipole. Respectively, the two magnetic poles form a large "magnetic spot". High-resolution spectra were obtained allowing He I and Si II abundance variations to be studied as a function of rotational phase. The results show that the helium abundance is concentrated in one hemisphere of the star, near the magnetic poles and it is comparatively weaker in another hemisphere, where magnetic field lines are horizontal with respect to the stellar surface. At the same time, the silicon abundance is greatest between longitudes of 180 - 320$^o$, the same place where the helium abundance is the weakest. These abundance variations (with rotational phase) support predictions made by the theory of atomic diffusion in the presence of a magnetic field. Simultaneously, these result support the possibility of the formation of unusual structures in stellar magnetic fields. Analysis of vertical stratification of the silicon and helium abundances shows that the boundaries of an abundance jump (in the two step model) are similar for each element; $\tau_{5000}$ = 0.8-1.2 for helium and 0.5-1.3 for silicon. The elemental abundances in the layers of effective formation of selected absorption lines for various phases are also correlated with the excitation energies of low transition levels: abundances are enhanced for higher excitation energy and higher optical depth within the applied model atmosphere.Comment: accepted by MN, 7 pagers, 10 figs, 3 table

Radiation and Protective Polymeric Dielectric Aggregates with Effect of the Active Protection

In case of electrical breakdown of dielectrics electromagnetic interferences can destabilize operation of the electronic equipment and instruments of aerospace complexes. In the conditions of space flight the initiated electrobit phenomena as a result of high-energy ionizing radiation, solar flashouts and radiation belts ofEarth, finally, lead to corrupting of dielectric materials, especially polymeric materials and aggregates. In operation the possibility of receiving constructional dielectric polymeric aggregates capable to remove the accumulated excess electrical charge, for protection of jackets of the electronic equipment of space aircraft is shown. Materials are received in the way joint dispersion of a polymeric matrix and reactivehydrophobic metallooligomer in the form of nanodispersible powders in a polymer melt with the subsequent solid-phase compaction under pressure. As the active fillers of polymeric aggregates high-dispersible radiation-hardened metallooligomer on the basis of bismuth polietilsilikonat, capable to be sewed chemically with polymeric matrixes as a result of radiation solid-phase polymerization are used. Keywords: polymer matrix, bismuth polyethylsilicone, dielectric composites, active protection, mechanoactivation, solid-phase compaction

Vsini-s for late-type stars from spectral synthesis in K-band region

We analyse medium-resolution spectra (R\sim 18000) of 19 late type dwarfs in order to determine vsini-s using synthetic rather than observational template spectra. For this purpose observational data around 2.2 $\mu$m of stars with spectral classes from G8V to M9.5V were modelled. We find that the Na I (2.2062 and 2.2090 $\mu$m) and $^{12}$CO 2-0 band features are modelled well enough to use for vsini determination without the need for a suitable observational template spectra. Within the limit of the resolution of our spectra, we use synthetic spectra templates to derive vsini values consistent with those derived in the optical regime using observed templates. We quantify the errors in our vsini determination due to incorrect choice of model parameters \Teff, log $g$, $v_{\rm micro}$, [Fe/H] or FWHM and show that they are typically less than 10 per cent. We note that the spectral resolution of our data(\sim 16 km/s) limited this study to relatively fast rotators and that resolutions of 60000 will required to access most late-type dwarfs.Comment: 8 pages, 4 figures, 3 tables, accepted to the MNRA