Avoiding the cascade of spurious frequencies in the analysis of stellar light curves

In the frequency analyses of stellar light curves the objective is to extract true pulsation frequencies down to the limit of the noise. It is well known, though, that this in practice is never reached. One of the most puzzling cases hampering the frequency analysis and preventing to reach this level of precision is the so-called cascade of spurious frequencies. This happens especially when the density of modes per frequency bin is high. Contrary to what is intuitive, a high signal-to-noise ratio can also be a factor influencing the appearance of spurious frequencies since sidelobes produced by the spectral window can be above the mean noise level. This has been shown by Balona 2014 and other authors. Mitigation strategies have been suggested but no general solution has been found so far to this phenomenon. Here we show with simulations and data from observations of Kepler satellite, that a simple solution is found by improving the fitting algorithm. The clear benefit of investing in a better fitting algorithm is finding the true pulsation frequencies, which is the first and mandatory step to perform asteroseismology. Thus, these results can be of significant interest for any future studies and, especially, high amplitude and high quality data of multimode pulsators.