A Finder Chart should have the following:
- The primary target should be clearly indicated. If the primary target is not visible (too faint or part of a diffuse object), an offset target or two should be provided. These should be clearly marked with their offsets clearly marked.
- The target name or OB name should be clearly indicated on the finder chart.
- North and East should be clearly indicated.
- The image should be rotated when possible such that the requested PA is “up”.
- The scale needs to be indicated by drawing a bar and writing the bar length in arcseconds or arcminutes.
- The wavelength range of the image should be indicated and should match that of the acquisition image taken at the LBT.
- The image should reach about the same depth as expected in an acquisition image at the LBT.
- The entire instrument acquisition FOV should be shown.
For brighter targets, a finder chart can be generated using modsView with the –finder option. By default modsView uses an image from the digitized sky survey, but if you have a FITS format image with a valid (and correct!) world coordinate system applied, you can use that image to create the finder. Using this method creates a 12′ x 12′ FOV finder, which is very large compared to the 1′ x 1′ longslit acquisition field. It is best to supplement this! It is best to use an SDSS image when possible. A 30 second MODS image is approximately the same depth as a SDSS image.
For faint targets, it can be useful to have charts that show the target in relation to nearby objects. Ensure that whatever source you use to obtain your image, that your finder chart meets all requirements listed above. Some images may clearly show the target, but if taken in an unsuitable wavelength or if no scale/orientation is shown, the clearest image will not be a suitable finder chart.