Tutorial on Visualizing Dithers of a Solar System Observation in APT

A tutorial on how to view dithers for a Solar System observation in the JWST Astronomer's Proposal Tool (APT) is presented in this article.

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See also: JWST Astronomers Proposal Tool Overview

Currently, APT does not have the capability to display an Aladin visualization of moving target dithers. Until such time that a fix is implemented, moving target observers can use a fixed target as a proxy to visualize their dithers. Accurate instrument field of view orientations can be determined using the Moving Target Visibility Tool (MTVT).

To learn how to download APT and start a JWST proposal, see the Moving Target APT Instructions. Before this tutorial, you may want to read Tutorial on Creating Solar System Targets in APT and Tutorial on Creating Solar System Observations in APT. If you have questions please contact the help desk.

Viewing dithers with a proxy moving target

In the example below, we define a fixed target, M-35 (an open cluster in the ecliptic), as a proxy for Callisto. Visualization of the instrument FOV, placement of the FOV for various dither and mosaic-tile offsets, and depth of coverage is then possible by changing (temporarily) the target of the observation from Callisto to M-35.

Switching targets in APT, for example, M-35 back to Callisto, will cause the Default Solar System target windows to repopulate. If you previously deleted any of the editable default target windows, you will have to do so again.

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

In order to visualize the dithers, click on the View in Aladin button at the top of the window. The Aladin viewer is discussed in the APT Aladin Viewer article.

Figure 1. Defining a fixed target proxy

Click on the figure for a larger view.

In the Aladin window, as shown in Figure 2, any observations you have highlighted in the left sidebar will be displayed over the sky catalog of your choice (DSS, 2MASS, Simbad, etc.). 

Figure 2. Viewing the observation in Aladin

Click on the figure for a larger view.

Pan and zoom to display at the level you want. Figure 3 shows a screenshot of a NIRCam subpixel dither. 
Figure 3. Visualizing a sub-pixel dither

Click on the figure for a larger view.


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