User manual

WHIRC Data Reduction Manual Version 2.0, 2014 June 26 35
just to make the separation of the input images in the output mosaic obvious (Figure
3.10). It is easy to identify the common stars in the mosaic.
Figure 3.10: Output image sak.j.mos.fits generated by the irmosaic task.
One can now display the mosaic image and run the apphot.center task on it by centering
the cursor on a star and hitting <spacebar> to measure the centroid. This must be done in
pairs, measuring the same star in two adjacent subimages in the mosaic image. Even if
the same star can be used in all images, it is important to maintain this order (e.g., ref star
in image 1; same star in image 2; ref star in image 2; same star in image 3, etc…). You
will end up with a text file of the sort ‘<mosaicimagename>.ctr.1’. Open up this file in
an editor and delete all lines except those with X and Y coordinates, which should be in
columns 1 and 2. Close the editor and write these two columns to a new file by the
command fields <mosaicimagename>.ctr.1 1,2 > <mosaicimagename>.coords.
This coordinate file can then be used as the input to the task irmatch2d (Figure 3.11).
The input image and database are those created by the irmosaic task, and the ‘coords’ file
is the coordinate file generated by the apphot.center task. The ‘alignme’ must be set to
‘coords’ to use the coordinate file input. The result is shown in Figure 3.12.