The rtft guide
rtft is the Real Time Fourier Transform program that provides
fast amplitude spectra of light curves obtained with rtp.
The program is currently non-interactive. One input file is given and
a few options are available. The output retains the format of the
rtp output files, with frequency in the first column, given in
micro Hertz, and data columns with amplitudes in micro modulation amplitudes
(mma).
rtft Startup
- In an xterm window, change directory to the data processing directory
for the run in question.
- Locate a file for Fourier processing.
This can be any light curve output from the rtp or rtcorr
programs. The ".raw" file is usually not very useful for processing, but
the ".dat" file can give sensible spectra when the conditions are photometric.
The ".dif" file gives useful spectra when the conditions are non-photometric.
- The rtft program requires the output range of frequencies to be
specified on the command line, together with the input light curve data file.
rtft 0 20000 phot.dif
- Useful options include -P to produce a power spectrum, -p to additionally
write lists of detected peaks (for each data column), and -N to suppress
normalization of the input data.
- The program produces a file with the ".sft" extension, and terminates.
To see the result, start gnuplot, and give a command like:
plot 'phot.sft' with lines
to see the resulting FT. The data column is easily selected in gnuplot
by specifying the column in the data file to use for the x:y axes,
for instance to plot the third data column
plot 'phot.sft' using 1:4 with lines
Data files
The rtft program normally produces only one output file with extension
".sft", containing the FT for all input columns.
However, with the -p option specified, peak
files are generated; one for each data column. These will have extensions
".pk0", ".pk1", ".pk2" etc.
Normalisation
rtft applies an automatic normalisation of the data (unless
the -N option is given). This implies fitting a least squares line through
the data points (for each data column) and subtracting, so that the input data
are always variations around zero.
Fourier algorithm
The algorithm used is a "slow" Fourier transform procedure adopted from the
qsft program.
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Last modified: Tuesday, 31-Apr-2001 12:08:31 ACT