Superflare G and K Stars and the Lithium abundance

We analyzed here the connection of superflares and the lithium abundance in G and K stars based on Li abundance determinations conducted with the echelle spectra of a full set of 280 stars obtained with the ELODIE spectrograph. For high-active stars we show a definite correlation between $\log A(Li)$ and the chromosphere activity. We show that sets of stars with high Li abundance and having superflares possess common properties. It relates, firstly, to stars with activity saturation. We consider the X-ray data for G, K, and M stars separately, and show that transition from a saturation mode to solar-type activity takes place at values of rotation periods 1.1, 3.3, and 7.2 days for G2, K4 and M3 spectral types, respectively. We discuss bimodal distribution of a number of G and K main-sequence stars versus an axial rotation and location of superflare stars with respect to other Kepler stars. We conclude that superflare G and K stars are mainly fast rotating young objects, but some of them belong to stars with solar-type activity. At the same time, we found a group of G stars with high Li content $(\log A(Li) = 1.5 - 3)$, but being slower rotators with rotation periods > 10 days, which are characterized by low chromospheric activity. This agrees with a large spread in Li abundances in superflare stars. A mechanism leading to this effect is discussed.Comment: 6 pages, 8 figures. The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the Su

Some aspects of comparing the operational properties of synchronous machines with a conventional and two mutually shifted excitation windings

A comparative analysis of the operational properties of traditional and two-valve synchronous machines with a rotor, having a reciprocating axis, excited from independent regulated DC sources, is generalized. On the basis of research, it has been shown that the use of a control quadrature excitation winding significantly improves the performance of synchronous machines at low costs for its manufacture. The authors have shown a significant improvement in the performance of machines with different operating modes based on the results of theoretical and experimental studies carried out on synchronous machines with a rotating axis of magnetic saturation, attached to various designs of quadrature excitation winding. It has been recognized that neglecting magnetic saturation in performance calculations for synchronous machines leads to significant estimation errors properties of the studied machine. In addition, the advantages of synchronous machines with sine-cosine field winding are shown. With an insignificant complication of the manufacturing technology, it opens the way to solving the problem of creating energy-saving turbine generators, which have a property that is very important for the practice of operation, i.e. an almost unchanged (sinusoidal) shape of the resulting magnetic field in the air gap of the machine within the allowable range of load variation under steady-state symmetric modes