97 research outputs found
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 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 , 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 comments on the matching of photometric and magnetic properties of structures at the solar surface
We investigate sharply outlined features recorded in solar magnetic field
tracers. It is shown that the magnetic boundaries of a sunspot do not coincide
with the photometric ones. Moreover, there is no clear magnetic boundary around
sunspots. Thus, the widely accepted concept of a magnetic tube with clearly
pronounced borders is not always correct and should be used with caution. It is
also shown that even in the periods of complete absence of visible spots on the
Sun, there are magnetic fields over 800 Gauss. The nature of these strong
magnetic fields remains unclear; they may originate at relatively small depths
under the photosphere.Comment: 6 pages, 2 figures. Proceedings of the Fifteenth Workshop "Solar
Influences on the Magnetosphere, Ionosphere and Atmosphere", Primorsko,
Bulgaria, June 202
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