Science Operations

Script Preparation

For each target, at least two LBC scripts (aka OBs, observing blocks) are needed:

  1. a co-pointing OB that is used to collimate and correct the pointing and the copointing of both sides of the telescope, while also maximizing the available range of the optics so that both collimation and copointing can be maintained throughout the observation without a mirror being driven into a limit; and
  2. a science OB that configures the instruments and executes a sequence of observations of the science target.

All scripts for LBC are in xml format and can be produced using the LBT Observing Tool (OT). (The Observing Block Creation GUI provided by the LBC team also remains available but the OT is strongly preferred).

Please see the pages under Script Preparation for the definitive guide to using the OT to prepare LBC scripts. What follows here is just a brief explanation of the scripts and materials needed.

For each target, you should include:

  • A co-pointing OB
    • one for each target
    • The co-pointing target should be a clearly identifiable catalog (e.g. UCAC5) star
      • with good coordinates;
      • near (within a degree [check]) of your science target
      • for which there are 5-6 stars suitable for collimation
        • these are stars with 15 < R < 16.5
  • A science OB or OBs
  • A finding chart of the co-pointing target, with target clearly identified – Required
  • A finding chart of your science field – Optional

Science OBs

Science OBs should be 30-40 minutes in length, after which time the telescopes will need to be collimated again (although the use of the Telescope Metrology System, TMS, enables longer intervals without re-collimation. See the LBC observing with TMS web pages [to be constructed; 2022-Oct-05] for more information about TMS).

A finding chart may be helpful if you are concerned about chip gaps, or saturation of specific objects, but is not required for science observations.

The collimation and co-pointing OB

Since LBC operates in a fully binocular sense it is critical to minimize the demands on the guide loop by making sure the mount correctly knows where it is pointing and ensuring the two sides are co-pointed. This is be achieved with a co-pointing OB, at or near your science target field.

Co-pointing target:

Select an easily identifiable (isolated, 12.8 < R < 14.5) source with low proper motion as the “co-point” target that you preset to in the co-point OB. This can be your science target itself if it meets the requirements, or a star in the same field, or if your science target is significantly extended it could be a nearby field. Provide a finding chart so that identification of the correct source is assured. Because the coordinate reference source is relatively bright, only a short exposure is needed for the pointing correction.

The co-pointing target is also used for collimation, and very crowded (i.e. Galactic plane) fields can be problematic for the collimation script (dohybrid/dofpia) as the out-of-focus pupils overlap. Select your fields carefully.

  • Choose a target that meets the following criteria:
    • The co-pointing target itself:
      • should have known, proper-motion corrected, coordinates
      • should be an unresolved point source (stars)
    • and the collimation region below the pointing center:
      • should contains 5-6 stars with 15<R<16.5;
      • but not be too crowded (otherwise the extra-focal pupils will overlap)
      • should be free of significant background gradients (large galaxies, nebulosity)
    • Example of a bad field for DOFPIA would be a large galaxy like M51 (like this)
      or a Globular Cluster
  • The LBC OT library contains examples and templates for the co-pointing observation. The parameters are:
    • Read full CHIP2 ccd, the others are not needed
    • 1.0 sec exposure
    • Use r-SLOAN (LBC-Red) and V-BESSEL (LBC-Blue), same as dofpia
  • Please don’t forget to include a finding chart which identifies the co-pointing target (a screen shot of chip 2 from the OT position editor would suffice).

Mixed Mode OBs

For mixed mode OBs please see: Mixed Mode LBC + LUCI/MODS

About LBC offsets

When preparing an LBC script in the OT, offsets can only be entered in Absolute DET X/Y coordinates. The OT will convert these to Absolute RA/Dec offsets (required by the LBCs) in the output script according to the following conversion:

where theta is the position angle.