Observing Procedure

The procedure for observing with the LBCs follows, for each new target, the sequence: collimate; copoint; and, finally, observe. Therefore, for each target, the PI should prepare not only the science OB(s) but also a “copointing/focus” OB which should have as its target a bright, easily identifiable, star with proper motion corrected coordinates and which should contain within the region of chip 2 that is used for collimation at least ~5 bright stars. Instructions on preparing a copointing OB can be found here.

The steps are detailed in each section, below:
Collimate
Co-Point
Run Science OB

Collimating

• • Load and run your copointing OB. Stop it and wait for a TMS update. You may take the pair of copointing images to assess image quality before collimating.
  • To collimate, run dofpia or dohybrid (if an old reference was used, dofpia should suffice).
  • In the Linux terminal window, run dofpia --X2 (or dohybrid --X2)
    • X2 doubles the exposure time to 32 seconds, and averages over seeing variations, but should not be used for fields near the zenith, i.e. at elevation > 85 deg).
    • If, for some reason, you have chosen to ONLY use LBCR or LBCB, add the option --RedOnly or --BlueOnly.

• Take the TMS referenceafter collimation:
  • ./lbc_set_tmsoffset.py -s 2 (for binocular mode; -s 0 for SX only and -s 1 for DX only)
    
• Start the TMS loop:
  • ./tms_loop.py

Once the tms_loop has been started, the loop will automatically pause and take a new reference after each collimation sequence completes.

• Collimation can be tricky when there is a large temperature differential across the mirror or between the mirror & air. dofpia/dohybrid have problems with fitting high order spherical. To turn it off, use dofpia in interactive mode; the response “z22” will negate the z22 correction.
• All of the options for dofpia are listed below. The syntax for their use is: dofpia --option
  • --x2 — this will take a 32-sec instead of 16-sec extra-focal pupil image. The longer image will average better over short time-scale seeing variations.
  • --backout — removes the initial z4/z11 values and takes no images. Use this when dofpia has failed to analyze pupils (e.g. because the sky is too bright or because of clouds) and exited.
  • --blueonly or --redonly — collimate only on the blue or red side. Useful when mixed-mode observations with the LBC and LUCI/MODS.
  • --askme   — prints the corrections that will be sent, but prompts the observer for a reply (“y”, “n” or “z22”):
    • “y” will cause all of the corrections to be sent and applied;
    • “n” will not send any of the corrections; and
    • “z22” will send send all of the corrections except for z22, and will remove its cross-talk contributions to z4 and z11.
  • --bypasstms  in case the background service which controls interaction between TMS and FPIA is not running. This service should always be running, even when TMS is not operational, so use of this option should be rare.

Co-Pointing

The copointing procedure adjusts the pointing model and the primary mirror to position the target as close as possible to the rotator center on each LBC while maintaining collimation and maximizing the range of travel available to the primary mirrors as they move according to a temperature and elevation dependent collimation look up table. This last goal explains the name of the LBTtools task that is used to copoint and range-balance, lbcrangebal.

lbcrangebal takes as input the pair of images generated by your copointing OB, yourCoint.ob