Folding Search - Phase Dispersion

   

The command FOLD/LIGHT_CURVE is available to perform a folding search on a binned data table. The data can have been corrected and manipulated in many ways: it is possible to specify the column containing the data to be folded. The algorithm used is the Phase Dispersion Method   described by [Stellingwerf1978]. For the determination of the significance of a detection please refer to the original paper. It is not possible to keep into account (or search for) a period derivative. The syntax of the command is:

FOLD/LIGHT_CURVE parfil

where: parfil is the name of the parameter file. The parameter file can be generated by calling CREATE/PARFIL with the option LFOLD (see Table 7.8). The meaning of the parameters shown in Table 7.8 are described below:

  
Table 7.8: Parameter file entries for FOLD/LIGHT

• N_OF_PHASE_BINS is the number of bins to fold the data into. The maximum number accepted is 100. Default is 20.
• INPUT_FILENAME is the input BDT table name. Default extension is TBL. There is no default.
• CENTRAL_PERIOD is the center value for the period range to be covered. There is no default value.
• PERIOD_STEP is the step on period. There is no default.
• OUTPUT_FILENAME is the filename of the output table containing the folded light curve corresponding to the best found period. A second table with the same name followed by _c will be created: it contains the statistical test (PDM) as a function od trial period. There is no default
• N_OF_PERIODS is the number of periods to test. If this parameter is set to 1, only one period (corresponding to the start period), is analyzed. Maximum value is 10000. Default value is 20.
• N_OF_PHASE_SAMPLES is the number of different coverages used. To smooth out effects due to the choice of a particular start phase (that is an epoch) a number of different sets of phase bins can be chosen. For a detailed explanation see Stellingwerf (1978). Maximum number is 10. Default value is 1.
• EPOCH is the epoch in SCC (or UTC for barycentric corrected tables) of the start bin of the folded light curve. It can be used for phase relating purposes. Default value is 0.0, but a value closer to the actual SCC arrival times should be used.
• TIME_COLUMN is the name (or number) of the column containing the times for the bins. According to the PROJECTION conventions, this time is used as starting time of the corresponding bin. Default is #1.
• DATA_COLUMN is the name (or number) of the column containing the data to be folded. Default is #2.
• ERROR_COLUMN is the name (or number) of the column containing the errors on the data. This information is NOT used in the period search, but only to propagate the errors in producing the output light curve folded to the best period. In case no error column is present in the data, the user can create an additional column filled with 0s. Default is #3.

• Format of the input: the files input to this command are:
  • PARAMETER FILE: standard ASCII file generated via CREATE/PARFIL.
  • DATA TABLE(S): they are BDTs as produced by the EXSAS projection and correction package. Their format is described in section 7.2.2. Notice that the data and error columns can be manipulated and corrected in many ways by the user.
• Format of the output: the files in output from this command are:
  • OUTPUT TABLES: the table named OUTPUT_FILENAME contains the light curve folded to the best period found. It is in the format of a MIDAS table with 3 columns: the first column always contains the phase (from 0.0 to 2.0); the second and third columns contain the data and error on data rate in the different phase bins. The table named OUTPUT_FILENAME_c contains the values of the PDM test as a function of trial period. The two columns contain the trial period and the PDM value respectively.
  • LOGFILE: it is an ASCII file containing a copy of the output to terminal. The logfile has the standard name stell.log