The “four sigma” limit for significant periodicities
Abstract
Most of the pulsations which have been observed
in sdB stars have very low amplitudes. Detection of modes
from photometric observations is usually performed by noting
the most prominent peaks in a periodogram or, equivalently,
an amplitude spectrum. A common strategy is to assume
that peaks which exceed four times the mean noise
level correspond to significant periodicities. The efficiency
of the assumption is investigated by simulation. It is found
that the actual significance levels corresponding to the four
sigma limit may vary by orders of magnitude, depending on
the exact data configuration.