Hello primitives

The first of these primitives is _IMAGING_HELLO_. It contains instrument-specific code and initialisation. It is best left alone. See preliminaries for a description of what this primitive does for each instrument.

Second there is a recipe-specific primitive such as _JITTER_SELF_FLAT_HELLO_. This sets up CCDPACK, sets directives when to perform certain operations, optionally create variances, removes any bias, and edits the FITS headers.

Two things you might wish to change in the recipe _HELLO script are listed below.

• Change the extent of the images. If there is an instrumental defect in some peripheral rows you might not want to use the full bounds as given by headers RDOUT_X1 ($x$ lower bound), RDOUT_X2 ($x$ upper bound), and RDOUT_Y1 and RDOUT_Y2 for $y$. Suppose you wanted to trim off the top three rows you could change the line.

      my $y2 = $Frm->hdr( "RDOUT_Y2" );
  

  to

      my $y2 = $Frm->hdr( "RDOUT_Y2" ) - 3;
  

• Switch on error propagation. To save time at the telescope, the pipeline does not keep track of the errors per pixel (except for the polarimetry recipes with names starting ``POL'' and the NOD_CHOP series). If you wish to know realistic errors for your data, in the recipe switch on the USEVAR argument for the recipe's _HELLO primitive. Here is an example for the BRIGHT_POINT_SOURCE recipe.

      _BRIGHT_POINT_SOURCE_HELLO_ USEVAR=1