Wavelet analysis of stellar rotation and other periodicities

D. B. de Freitas, I. de C. Leão, B. L. Canto Martins, J. R. De Medeiros

Published 2010-09-26Version 1

The wavelet transform has been used for numerous studies in astrophysics, including signal--noise periodicity and decomposition as well as the signature of differential rotation in stellar light curves. In the present work, we apply the Morlet wavelet with an adjustable parameter $a$, which can be fine-tuned to produce optimal resolutions of time and frequency, and the Haar wavelet for decomposition at levels of light curves. We use the WaveLab--package (library of Matlab routines for wavelet analysis) for the decomposition and a modified version of Colorado--package for the wavelet maps of synthetic and observed light curve. From different applications, including Virgo/SoHO, NSO/Kitt Peak, Voyager 1 and Sunspot data and synthetic light curve produced by different simulators, we show that this technique is a solid procedure to extract the stellar rotation period and possible variations due to active regions evolution. In this paper we show the Morlet Wavelet Amplitude Maps, respectively corresponding to oscillations in the photospheric magnetic field of the Sun (NSO/Kitt Peak data), the daily averages of the magnetic field strength B versus time measured by Voyager 1 (V1) during 1978, and synthetic light curve produced by A. F. Lanza. We can also identify the noise level, as well as the contribution for the light curves produced by intensity, variability and mean lifetime of spots. Thus, we can identify clearly the temporal evolution of the rotation period in relation to other periodicity phenomena affecting stellar light curves. In this context, because the wavelet technique is a powerful tool to solve, in particular, not trivial cases of light curves, we are confident that such a procedure will play an important role on the CoRoT data analysis.