Finder Chart Guidelines

In most cases Tim’s Finder Chart Tool is adequate.

We highly recommend using it for ALL blocks and especially MOS observations.

If however, your target is not obvious or too faint in those produced by this tool, you are strongly advised to prepare additional finder charts (e.g. a zoomed in view).

If your target is too faint for the acquisition camera (for details see the Call for Proposals Document), then you must add a reference star on the slit and choose the appropriate Position Angle to place that star and your target on the slit. During acquisition we will centre the slit on the reference star, automatically putting your faint object on the slit.

Additional finder charts should meet the following criteria

Please provide good quality JPEG, PNG or PDF finding charts, at least 500×500 pixels in size. They should be readable both on-screen and printed, and have the following attributes and information marked on them:

  • Black sources on a white background.
  • Proposal ID
  • PI name
  • Target name and target identified clearly (e.g. circled, arrowed)
  • Field of view of ~10′x10′, with additional blow-ups (in a separate file) if more accurate information is needed.
  • Scale of the image (a bar showing its length in arcsec/arcmin).
  • Orientation of North and East (using a compass).
  • Position angle (for slotmode, longslit and MOS observations). Please see the Tips and Tricks page for some instructions on calculating the Position angle.
  • The filter used for the image e.g. V band, R band, H-alpha. Images in non-visible bands (eg. K-band) should be avoided if possible, as they cannot be directly compared to the acquisition camera. If using a DSS image, you still need to specify which photographic band (in most cases this will be ‘DSS blue’, ‘DSS red’ or ‘DSS infrared’).
  • The target position must clearly and unambiguously marked using an arrow, circle, box or similar. If necessary, add a second chart with a zoomed-in view.
  • Colours might be useful on screen, but be aware that we print only greyscale.
  • If you really must make an additional MOS finder chart, please mark the targets and the reference stars with different symbols, making sure it is all legible.
  • Any other observing mode dependent info (e.g. circling comparison stars).

Other Resources

  • Image Mosaic Service – lets you create very large images from a variety of surveys. May be useful to create e.g. 10×10 arcmin 2MASS J-band images if photographic sky survey material is saturated.