Zero-mean adjustment

The keyword sim:zeromean may be used to adjust the mean value of the time series (or a subset) to zero. It is given with two floating-point parameters,

1. the lower time limit, and
2. the upper time limit.

If the lower and upper time limits are both set zero, the mean value of the entire synthetic time series is adjusted to zero. This option was adopted for consistency, but does not provide additional functionality, because a zero-mean correction of the whole data set is performed at every step of the prewhitening cascade by default.

Example. In the sample project sim-zeromean, SIGSPEC models the same time series as in the project sim-poly (p.), according to the first part of the file sim-zeromean.ini:

Figure 36: Time series generated by the simulator in the sample project sim-zeromean. The sampling represents the V photometry of IC4996#89. First the simulator generates a set of power functions over intervals within the time series (grey), then the actual light curve (black) is produced by shifting the mean observable for each power function to zero individually.

sim:poly   2520.215 2521.088 4.298 2520.626  0.581
sim:poly   2521.088 2521.679 2.932 2521.443  1.195
sim:poly   2521.679 2522.442 1.092 2522.067  1.063
sim:poly   2522.442 2522.595 5.372 2522.466  0.676
sim:poly   2522.595 2523.351 2.495 2522.682  2.042
sim:poly   2523.351 2523.924 2.839 2523.607  0.221
sim:poly   2523.924 2524.478 8.357 2525.412 -0.899
sim:poly   2524.478 2525.399 2.304 2524.576  1.432
sim:poly   2525.399 2526.107 2.573 2525.721  1.205
sim:poly   2526.107 2526.550 6.350 2526.493  0.031
sim:poly   2526.550 2526.847 4.192 2526.589  2.893
sim:poly   2526.847 2527.616 0.345 2527.652 -0.472
sim:poly   2527.616 2528.264 3.583 2527.783  0.725
sim:poly   2528.264 2528.777 1.246 2528.704  0.610
sim:poly   2528.777 2529.606 3.534 2529.535  1.752
sim:poly   2529.606 2530.242 9.002 2529.694  1.119

This block of sim:poly keywords is followed by a corresponding block of sim:zeromean keywords:

sim:zeromean   2520.215 2521.088
sim:zeromean   2521.088 2521.679
sim:zeromean   2521.679 2522.442
sim:zeromean   2522.442 2522.595
sim:zeromean   2522.595 2523.351
sim:zeromean   2523.351 2523.924
sim:zeromean   2523.924 2524.478
sim:zeromean   2524.478 2525.399
sim:zeromean   2525.399 2526.107
sim:zeromean   2526.107 2526.550
sim:zeromean   2526.550 2526.847
sim:zeromean   2526.847 2527.616
sim:zeromean   2527.616 2528.264
sim:zeromean   2528.264 2528.777
sim:zeromean   2528.777 2529.606
sim:zeromean   2529.606 2530.242

This block is responsible for shifting the mean observable to zero for each synthesized power function.

Fig.36 compares the corresponding light curve with the light curve generated in the project sim-poly. (See also Fig.29) The 16 significant signal components detected by SIGSPEC are of minor interest and not discussed here.