4 Displaying and despiking the data

The command qdraw uses the Kappa routine linplot to display clearly the concatenated photometric data values. If you wish to plot the data in a different format then linplot will do the job (making sure that the Kappa tasks are initialised using the kappa command; refer to the documentation or type linplot prompt to see the available options. However, qdraw is recommended owing to the ease with which data can subsequently be despiked.

To plot the data simply type

  % qdraw <filename> mode=4 device=xwindows

where the input file is the output of scucat. This will give a plot of the data with the ordinate autoscaled to 5σ either side of the mean. Note that any data points further than 5σ from the mean are effectively hidden from you. The mean level and the ±3σ levels are indicated by dashed lines and error bars are suppressed for clarity. Numerical values of the mean signal, standard deviation and error in the mean are given for the full data set and the data set after clipping at the 3σ level. The qdraw routine will accept the same options as linplot so refer to the documentation if you wish to change the display parameters.

Further clipping can then be performed with the Kappa command drawsig. For example,

  % drawsig nsigma=2.5 device=xwindows

will clip the data at the 2.5σ level, again indicated by dashed lines on the plot and the statistics for the new clipping level will be given as before.

It is also possible that the data set will contain one or more large spikes in which case an iterative despiking method would be the best choice. In this case a new binary file with the bad points removed can be created with the command sigclip, e.g.

  % sigclip <filename> 3.0

will clip the data at 3σ creating a new file of the form filename_clip.sdf which can then be plotted with qdraw and drawsig.