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Paper: Spots and Activity of A-type Stars
Volume: 518, Physics of Magnetic Stars
Page: 131
Authors: Savanov, I. S.
Abstract: We estimate spottedness of surfaces of A stars from the rotation modulation of Kepler light curves. We distinguished two groups of stars—the first of them has the value of the spottedness parameter S more than 0.001 and the second—less than this value. Almost all objects of type ROTD (stars with a characteristic pattern with a broad peak and a sharp peak at a slightly higher frequency) fall into the second group. We investigate relations between parameter S, Teff and rotational period P and suggest the possibility of existence of the general trend in the changes in S with Teff. A detailed analysis of the spot activity of several A stars was started, first results are presented here. We derived rotation periods of spots on the stellar surfaces and studied the evolution of spot positions. Additionally we perform the analysis of the brightness variability of several A stars belonging to objects of the ROTD type. We concluded that the peak corresponding to the sharp peak is dominant because it is present on the periodograms for each set of observations, and the positions and amplitudes of the other peaks undergo changes and form a set of peaks on the resulting periodgram with smaller amplitudes. Assuming the presence of differential rotation for the studied stars of the ROTD type we found the values of the parameter ΔΩ and compared them with the available data from literary sources. There are indications of a fast evolution of spots on time scales of the duration of the Kepler observation set of 90 days. Our results can be considered as possible indications that localized magnetic fields in A stars might exist, although these stars possess radiative stellar envelopes.
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