Spots and the Activity of M Dwarfs from Observations with the Kepler Space Telescopeстатья
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Аннотация:Abstract—A method for estimating the spottedness parameter S (the spotted area as a fraction of the
surface of an active star) proposed earlier is applied to an analysis of activity in 1570 M dwarf stars. The
analysis is based on observational material obtained with the Kepler Space Telescope, as well as data
on the fluxes of the studied objects in the near and far ultraviolet (NUV and FUV) based on data from
the GALEX space telescope. The variations of S with the ages of the stars are studied (four groups
with different ages are distinguished), as well as variations of S with their rotational periods. A diagram
characterizing the relationship between S and the Rossby number Ro resembles the classical dependence
of the X-ray luminosities of active stars on Ro, and a saturation regime is attained at the same value,
Ro = 0.13. Moreover, objects with ages of more than 100 million years do not form a single sequence
(and stars older than 900 million years possess surface spottednesses of order 1%). The S−Ro dependence
obtained could expand possibilities for analyzing the dependence of the X-ray luminosities of active stars on
their Rossby numbers, and could also be applied to refine parameters characterizing the action of dynamo
mechanisms, such as the dynamo number ND. A comparison of the GALEX NUV and FUV brightness
estimates with the activity parameters of the stars suggests that younger, more rapidly rotating active stars
are brighter in the NUV, and that the FUV flux grows and the difference of the FUV and NUV brightnesses
decreases with increasing spottedness S.