The evolution of solar-like activity of low-mass stars |
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Authors: | M M Katsova and M A Livshits |
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Institution: | (1) Astrophysics Division of ESA's Research and Science Support Department -, P.O.Box 299, 2200 AG Noordwijk, The Netherlands;(2) Vaiana - Piazza Parlamento I, 90134 Palermo, Italy |
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Abstract: | An analysis of data on chromospheric activity obtained in the framework of exoplanet-search programs is presented. Observations
of 1334 stars showing that the chromospheric activity of the Sun is clearly higher than for the vast majority of stars in
the solar vicinity are used. A comparison of chromospheric and coronal activity led to the identification of a significant
group of stars with a low level of chromospheric activity, whose coronal radiation spans wide ranges. There are reasons to
believe that the chromospheric and coronal activities of one group of stars decrease simultaneously as the rotation decelerates,
while, in stars of the other group, the chromospheric activity diminishes, but their coronas remain stronger than that of
the Sun. Features of cyclic activity of the Sun are discussed. This enables us to associate differences in the behavior of
the activity with different depths of the convective zones of stars of spectral classes earlier and later than G6. Arguments
in favor of a two-layer dynamo and different roles of the large-scale and small-scale magnetic fields in the formation and
evolution of activity are formulated. Age estimations based on activity levels (gyrochronology) must be carried out differently
for these different groups of stars. |
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