Instructions for LGS-AO observers


An LGS-AO observing run requires more preparation time than NGSAO from both the observer and the observing support team. It also requires substantial coordination with the Keck observing support team to plan the observations. We encourage you to read and follow the instructions below.

The primary contact person for LGS-AO science scheduling and support is you support astronomer. Please, contact him/her for any questions/suggestions regarding these instructions and your run preparation.

For more information, please contact the instrument scientists.


A. Prior to the run
  1. Formulate an observing plan and consider each of the issues below prior to the science planning teleconference.
    1. Target scientific priority.
    2. TT reference R magnitude.
    3. Both imaging and spectroscopy with NIRC2 are possible, using both fixed stars and moving objects as TT references. Limiting magnitudes and camera performance should be identical to those in NGSAO mode. The following documents may be useful for signal-to-noise estimation:
    4. Elevation constraints (20° in east, 36.8° in west, and see pupil rotation constraints page for zenith constraints).
    5. Is the TT reference extended or binary?
    6. Target identification strategy (initial images in wide camera, etc.)
    7. Observing wavelength.
    8. Is a certain PA or VA required?
    9. Observing scripts to be used (bxyn, manual dither, custom scripts, etc.)
    10. Minimum total integration time required.
    11. Required calibrations (twilight, photometric, sky frames, astrometric, etc.)

  2. Create a prioritized target list.
    1. Identify a suitable AO guide star using the AO guide star tool
    2. The target list must follow the LGS-AO format described here.
      Several extra fields must also accompany each target in the observer's target list, specifying the tip-tilt reference star to be used. Once you have created a list, please verify and submit it with the target list checker
    3. Software to assist in the identification of TT reference stars can be down-loaded from the software distribution page.
    4. For off-axis observations (r>30arcsec ): is the TT reference star in the field of regard of the tip-tilt sensor?
      Use the AO guide star tool or the TSS view tool to check or estimate the optimal sky PA angle.
    5. Please confirm the existence of the TT reference stars using the DSS or other image catalogues. Quite a number of reference TT stars turn out to be galaxies.
    6. The TT reference star must not be brighter than 8th magnitude.

  3. Plan NGSAO backup program(s).
    1. Please, read the instrument backup policy
    2. Also, review LGS-AO restrictions and procedures listed in KAON 269.
    3. And be aware of LGS-AO Weather Cancellation Policy approved by the Observatory Management.

  4. Science planning telecon with the Observing Support team to discuss the details of your observing plan and the status of the LGS-AO system.
    Please invite your collaborators if you wish. You will be contacted by the support astronomer 7 to 10 days before your observations. Items to be discussed:
    1. Observing plan and target list.
    2. Any issues relevant to off-axis targets, targets with high proper motions, etc.
    3. Backup NGSAO plan.
    4. Any questions you may have regarding operations, performance, etc.

  5. Send final LGS-AO target lists to the support astronomer
  6. 3 business days prior to observations.
B. Day of observing:
  1. Meet with the support astronomer at 2:30pm for an introduction to NIRC2, observing scripts specific to LGS-AO, use of on-site planning software (TSS widget), checking and loading the target list for the night, etc.
  2. The observing support team will perform AO calibrations 3-4:30pm (no access to NIRC2 during this time).
  3. Dome flats and darks may be taken by the observer from 4:30pm until sunset.
  4. An observing status meeting with the observing support team will be held at 4:00pm.
C. Observations:
  1. The observatory must comply with US Space Command, Federal Aviation Administration, and Mauna Kea Observatories policies regarding outdoor laser projection. All targets must be pre-screened by the US Space Command, with possible laser black-out periods enforced to avoid blinding surveillance spacecraft.
    1. Please read the summary of laser propagation restrictions and procedures for more information.
    2. Laser propagation is restricted from 8° evening twilight to 8° morning twilight.(15min before and after sunrise and sunset)
    3. The use of laser aircraft safety spotters is required and when a full compliment of spotters are not available due to illness, etc., the Single Spotter Policy will be followed.

    4. Evening twilight and the first 30 min. of the night (counted from 8° twilight) are used by the LGS-AO operations team to check the instrument, align the laser, and characterize the Na layer. This usually precludes taking evening twilight flats.
      Please, let us know if evening twilight flats are required for the science program, in which case we would plan on delaying our LGSAO instrument checkout.

  2. LGS-AO Acquisition of targets:
    1. We recommend reading the LGS-AO acquisition procedure that provides details about the roles of the summit OA, the LGSAO operator and Observers during acquisition.
    2. For faint tip-tilt reference stars (R>16), identifying the star in the 2' field of the acquisition camera is often a significant source of overhead. Please bring finding charts for all faint tip-tilt reference stars and help the observing assistant identify the TT reference star.
    3. Once the TT reference identified and centered, the LGS-AO operator will acquire the target optimize the correction, and will operate NIRC2 during this time.
      Acquisition of a new target in LGS-AO is somewhat complex, due to the requirement that two properties of the Na layer must be determined before science integrations can begin. One is the altitude of the layer, the other is the effect of the layer's structure and thickness on the wavefront measured by the WFS. Both of these are determined iteratively by observing the wavefront of a natural guide star with the LBWFS while locked on the LGS with the WFS.
    4. Typical LGS-AO acquisition sequence:
      1. Slew to science target.
      2. Identify and acquire TT reference, close TT loop.
      3. Project laser towards TT reference star, close DM loop on LGS.
      4. Start LBWFS operations to record images and control focus on TT reference star.
      5. Optimize WFS centroids (image sharpening) and Na altitude using LBWFS.
      6. Since LBWFS integrations are necessarily long when using a very faint TT reference (R-mag>19), the initial determination of these properties maybe more efficiently done on a bright star prior to acquisition of the science target.
      7. Offset to science target, hand control over to the observer to begin science operations with NIRC2/OSIRIS.
    5. When acquisition is complete, the LGS-AO operator will hand the control of NIRC2/OSIRIS to the observer.

  3. NIRC2 operations:
    1. The operation of the NIRC2 camera is identical in LGS-AO as in NGSAO, and most NIRC2 commands which interact with the telescope and AO system (such as nod or bxy5 2.5 2.5 n=2) will appear to behave identically. The principal differences in operation are the significantly higher overhead involved in target acquisition, the higher probability of interruption of long integrations, and the more extensive region of poor performance near zenith.
    2. See NIRC2 online documentation.

  4. LGS-AO overheads:
    These numbers reflect performance as of May 2005.
    AO & laser startup (from 12° twilight) 30 min
    Acquisition of new target (TT ref. R<15.5) 3-5 min
    Acquisition of new target (TT ref. 15.5 < R < 17.0) 5-8 min
    Acquisition of new target (TT ref. R>17.0) 6-10 min
    Dither with laser move 20 sec
    Dither without laser move 10 sec
    Recovery from aircraft or LTCS shuttering of the laser 3 min

  5. We encourage you to keep an accurate log of the observing science frames and other AO parameters. Note however that many useful AO and laser parameters are recorded in the NIRC2 headers. The LGS-AO support team will log AO, laser, and atmospheric characterization data.
C. Post-observing:
  1. Data backup: The observers are responsible for the backup of the science data for their own use. A separate copy of the science and engineering data will be backed up by the support team and archived at HQ.
  2. The observers should make a copy of their logs available to the LGS-AO support team, to assist in the engineering analysis of the science data.
  3. Observers should fill out a post-observing comment form. We welcome your feedback and suggestions for technical and procedural improvements to the LGS-AO system.
  4. We are devoting considerable resources to understanding and improving LGS-AO performance. Please help by sending us the results of any analysis of AO performance or observing efficiency which you perform with your science data.
  5. Authorship policies and suggested acknowledgments can be found here.