2.4.2 Enter Target Information

With any Spitzer AOT, the target name and coordinates are entered first. As this step is common to any observing proposal, we will provide a bit more detail on target entry in this chapter.

We first launch Spot and bring up the new target window, either by positioning the mouse over the target icon (the bulls-eye icon on the taskbar; see Fig. 2.1), or by selecting ``new target'' from the ``Targets'' menu. The target entry window will appear, with entry dialog as shown in Fig. 2.2.

Figure 2.2: The target entry dialog.

Several features are accessed from the target entry window. These include:

1. Resolve the name: NED/SIMBAD target name resolution. Simply enter the name of the target for which you want the coordinates, select the resolver (NED or SIMBAD), and click ``Resolve the Name.''

2. Visibility/Orientation Determine visibility windows for inertial and moving targets.

3. Background: Sky background estimates for inertial targets. You have the option of specifying the wavelength at which to estimate the background, as well as performing the calculation for a specific date, or over the entire range when the object is visible to Spitzer.

4. Option to avoid bright moving objects that might be in the target field. Bright objects to be avoided include both the Earth/Moon and `Others', which are Mars, Jupiter, Saturn, Uranus, Neptune and the asteroids Vesta, Hebe, Ceres, Iris, and Eunomia. Selecting these options will restrict the observations to preclude times when the target coordinates are within $7^\circ$ of the Earth and Moon, or within $30^\prime$ of the objects on the `Others' list.

In the target entry dialog, there are two general choices for the type of target (fixed or moving), displayed under five tabs. For fixed targets, these are: Fixed Single, Fixed Cluster, and Fixed Cluster - positions. For moving targets, these are Moving Single, and Moving Cluster. See Fig. 2.2. These are described in more detail below:

1. Fixed Single: A fixed-single target is one object or map center outside of the Solar System.

2. Fixed Cluster: A Spot `cluster' does not necessarily mean an astronomical cluster. Rather it defines a group of positions in a region of sky within a radius of $1^\circ$ to be observed with the same AOT parameters. Targets of this type are sets of objects that have a scientific requirement for observation in close spatial and temporal proximity. By using cluster targets you avoid the per AOR slew tax you might otherwise incur by having separate fixed single targets. The positions are entered as a primary equatorial J2000 right ascension and declination, and the offsets north and east from the primary target. Note that the east offsets DO NOT follow lines of declination on the celestial sphere. North and east are determined at the primary target position when the observation starts. If it is crucial for your science that you have an exact RA and DEC, you should use a Fixed Cluster - positions target type.

3. Fixed Cluster-positions: Defines multiple absolute positions where no two positions are separated by more than $2^\circ$.

4. Moving Single: A moving single target is a single object that requires Solar System tracking.

5. Moving Cluster: A group of co-moving Solar System targets separated by less than $1^\circ$ to be observed with the same AOT parameters. The positions are entered as a primary target and offsets east and north from that position. The ephemeris for the primary target determines the tracking rate to be used for the entire cluster, but the primary target itself does not have to be observed as part of the cluster.

A few words about overhead and the ``cluster'' target type: The cluster option has the advantage of saving a significant amount of overhead in some types of programs (e.g., some IRS Peak-Up overheads; see Chapter 6). Any set of observations which can be carried out as a cluster target could also be carried out as a string of observations of Fixed Single targets and a set of AORs. Providing science goals can be met, the ``cluster'' target allows the user to utilize only one AOR. However, the flight software is built in such a way that doing it as a set of Fixed Single observations can incur additional overhead for each new target (e.g., for target acquisition).