This document shows how to create POS TARGs with Aladin (click here to see the movie), and how to save these values directly into the proposal. The project is to image 3 filaments in the Cas A supernova remnant with the WFC3/IR camera. We have HST images available which we will use to determine the placement of the apertures. We have measured the position of a star in the field, and will determine offsets from that star to the filaments.

We have already loaded in the 3 HST images, as well as the DSS image, into Aladin. The Multiview 4-panel mode has been selected to display all 4 images in the Aladin display. Note that the aperture is centered on the measured star, and that Exposure 1 is selected.

In the APT window, select the Create POS TARG mode option. In the Aladin window, drag and place the aperture on the first filament of interest. Note the line drawn from the star to the filament, indicating a POS TARG has been created, and that the POS TARG appears on all 4 images.

Select exposures 2 and 3 and places the apertures on the remaining 2 filaments. In the APT window, you will see the POS TARGs in the pending changes area.

You could select all the changes individually, select the Visit, or select the Commit All option to save the changes to the proposal; similarly, if you did not like the changes, you could clear them as well.

With the Visit container selected in the APT Tree Editor, go back to the Aladin window to review the results.

If you want to see the detector X-Y axes, click on the POS TARG XY Axes button in the APT window.

Note that the POS TARG values we have generated will only place the aperture on the filaments for the ORIENT value we had when we made the POS TARGs. You should be sure to have specified that exact ORIENT value in your proposal.

Last modified: May 30, 2014.