Adding a Target observation

First of all, you have to decide which of the observations in the template library is most appropriate for your target. For point sources, this is probably point source, nod along slit. For extended sources, you'll want extended source, nod to blank sky. If you are in doubt as to which sequence to use, ask your support scientist or contact the CGS4 instrument scientist for advice.Drag the one you want from the template library into your science program. As an example here, we'll use the point source, nod along slit one. Drop it so as to appear after your standard star.

Now, in your science program, double click on where it says "point source, not along slit" and in the editor panel that pops up, type in a title for this observation. This isn't used as the target name or anything, it's for your own reference, and should be reasonaby descriptive as you will choose this name from a list of your observations to specify that this is the one you want to observe.

Setting the target co-ordinates etc

Now click the little handle next to your target observation to expand the view, and click on the "Target List" component. In the panel that appears, fill in your target name (this is what will go into the data headers etc) and the RA and Dec of your target. If you wish, you can enter a target name and click the "Resolve" button to have the OT query the target name on SIMBAD and get the co-ordinates from there. If you want the name resolver to query an different database, simply select it in the pull down to the left of the resolve button.

Next, we'll go into the plot window to check things and to set a guide star etc. Click on the "Plot" button in the lower left of the target editor window. In the window that appears, go into the "Calalog" menu and under "Image Servers", select "Digitised Sky at JAC". After a pause and some flashing lights, a digitised sky survey image of the sky area you're looking at should fill in. To the lower left of the image are a set of togle buttons, collectively labeled "View". Turn on the ones for "Sci Area" - shows the slit, "Dichroic" and "X-head" - the latter two between them show you the area of sky from which you can select a guide star. Now go to the "Catalog" menu again and under "Catalogs", select "Guide star catalog at CADC". When the progres box disapears, a list of HST guide stars will have been loaded. Turn on the "Catalog" view button, and these will be highlighted on the sky survey image. To manually inspect the list of stars, select "Browse" from the "Catalog" menu.

To the left of the window, there's a selection of buttons labeled "Mode". Click on the one labeled "GUIDE", now point and click on the star that you wish to use as a guide star. If you select one of the ones from the catalog, the positions from the calalog will be used. If you prefer, you can just click on a star at any position on the sky survey image. If you're doing this, then you might want to use the zoom facility to give you more accuracy. You must select a star that is within the purple X-head circles (and avoid ones close to the edge as you're going to be nodding) and not hidden by the green dichroic edges (again, and not too close).The position editor window should now look something like this:

Returning to the target editor panel in your science program window, you'll notice that it has filled in the guide star co-ordinates you chose, and if you edited your position using the "drag" facility, the co-ordinates have updated.

Setting Exposure times etc

Next, go back to the flat and arc observation and copy the CGS4 component again. Replace the one in your target observation with this, then go into it and set the magnitude or exposure time that you wish to use.

Note: The BL option in the magnitude pull down selects the minimum time necessary to become background limited. You might want to observe for longer than this, but bear in mind that the time between nods equalls this time multiplied by the coadds and the sampling. See the CGS4 handbook for more details.

The sequence

The only thing you'll usually wish to change in the sequence is the number of repeats. The "Offset" itterator executes a 4 position jitter (Object - Sky - Sky - Object). The repeat iterator sets how many times to repeat this sequence. Simply double click the repeat iterator and set the number.