Natureza multifractal da atividade magnética em estrelas tipo solar observadas pela missão Kepler

Abstract

In the present work we investigate the multifractal nature in time series of stars observed by the Kepler mission, for a sample of 651 stars that exhibit some quarter with low magnetic activity, using the Multifractal Detrending Moving Average (MFDMA), which allow detecting signals of multifractality in non stationary time series. Used different multifractal indices based on the geometric profile of the spectrum of multifractality, to estimate possible correlations between inactive phase characteristics of the star and the referred indices. From the multifractal point of view, as the Hurst exponent, extracted from the multifractal spectrum, is related to the long-term signatures in the time series, it is expected that it will be able to separate the sample into two populations, active phase and inactive phase. In the literature, it has been shown that the Hurst exponent has a strong connection with the rotation period, therefore, it can also be used to establish some kind of adequate calibration to estimate the period of rotation of stars that do not exhibit rotational modulation. As a result, our research presents an unprecedented outcome and opens a new way for estimating rotation period for stars with weak magnetic activity. Nevertheless, our results warn that a calibration that can give us the period of rotation of inactive stars is possible only when we have a sample that carries at least one magnetic cycle.