For the ``long'' power spectra the plot is not a feasible way to look
for significant peaks. A command is present to identify in the power
spectrum bins with a significance above a certain threshold.
The command DETECT/PERIOD
takes in input a ``long'' power spectrum produced by the command
MAKE/POWER_SPECTRUM (LONG option)
and gives in output all the bins
whose probability to occur by chance in that power spectrum
(keeping into account the number of trials) exceeds a given threshold.
The chance probability at a given frequency 
is defined as
where N is the number of trials and 
is the cumulative
chi-square probability function corresponding to 
degrees of
freedom.
The input parameters are the name of the table containing the power
spectrum and the threshold for the chance probability 
.
The informations (frequency, error on frequency, power and chance
probability) about the bins whose chance probability t
exceeds the input value 
will be displayed in output.
The syntax of the command is:
DETECT/PERIOD ps_table signifwhere ps_table is the input table containing the power spectrum and signif is the threshold probability.