  We present our analysis of simulated data in order to derive a detection
threshold which can be used in the pre-whitening process of amplitude spectra.
In case of ground-based data of pulsating stars, this threshold is
conventionally taken to be four times the mean noise level in an amplitude
spectrum. This threshold is questionable when space-based data are analyzed.
Our effort is aimed at revising this threshold in the case of continuous 90-day
Kepler K2 phase observations. Our result clearly shows that a 95% confidence
level, common for ground observations, can be reached at 5.4 times the mean
noise level and is coverage dependent. In addition, this threshold varies
between 4.8 and 5.7, if the number of cadences is changed. This conclusion
should secure further pre-whitening and helps to avoid over-interpretation of
spectra of pulsating stars observed with the Kepler spacecraft during K2 phase.
We compare our results with the standard approach widely used in the
literature.
