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
- Formulate an observing plan and consider each of the issues below
prior to the science planning teleconference.
- Target scientific priority.
- TT reference R magnitude.
- 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:
- Elevation constraints (20° in east, 36.8° in west,
and see pupil rotation constraints
page for zenith constraints).
- Is the TT reference extended or binary?
- Target identification strategy (initial images in wide camera, etc.)
- Observing wavelength.
- Is a certain PA or VA required?
- Observing scripts to be used (bxyn, manual dither, custom scripts,
- Minimum total integration time required.
- Required calibrations (twilight, photometric, sky frames,
- Create a prioritized target list.
- Identify a suitable AO guide star using
AO guide star tool
- The target list must follow the LGS-AO format described
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
- Software to assist in the identification of TT reference stars
can be down-loaded from the software distribution
- 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.
- 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.
- The TT reference star must not be brighter than 8th magnitude.
- Plan NGSAO backup program(s).
- Please, read the instrument backup policy
- Also, review LGS-AO restrictions and procedures listed in
- And be aware of LGS-AO Weather Cancellation Policy approved by the Observatory Management.
- 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:
- Observing plan and target list.
- Any issues relevant to off-axis targets, targets with high proper motions, etc.
- Backup NGSAO plan.
- Any questions you may have regarding operations, performance, etc.
- Send final LGS-AO target lists to the support astronomer
- 3 business days prior
B. Day of observing:
- 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.
- The observing support team will perform AO calibrations 3-4:30pm (no access
to NIRC2 during this time).
- Dome flats and darks may be taken by the observer from 4:30pm until
- An observing status meeting with the observing support team will be held at 4:00pm.
- The observatory must comply with US Space Command, Federal Aviation
Administration, and Mauna Kea Observatories policies regarding outdoor laser
All targets must be pre-screened by the US Space Command, with possible
laser black-out periods enforced to avoid blinding surveillance spacecraft.
- Please read the
summary of laser propagation restrictions
and procedures for more information.
- Laser propagation is restricted from 8°
evening twilight to 8° morning twilight.(15min before and after sunrise and sunset)
- 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.
- 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
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
- LGS-AO Acquisition of targets:
- 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.
- 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.
- 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.
- Typical LGS-AO acquisition sequence:
- Slew to science target.
- Identify and acquire TT reference, close TT loop.
- Project laser towards TT reference star, close DM loop on LGS.
- Start LBWFS operations to record images and control focus on TT reference star.
- Optimize WFS centroids (image sharpening)
and Na altitude using LBWFS.
- 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
- Offset to science target, hand control over to the observer
to begin science operations with NIRC2/OSIRIS.
- When acquisition is complete, the LGS-AO operator will hand the control of NIRC2/OSIRIS to
- NIRC2 operations:
- 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
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
- See NIRC2 online documentation.
- LGS-AO overheads:
These numbers reflect performance as of May 2005.
|AO & laser startup (from 12° twilight)
|Acquisition of new target (TT ref. R<15.5)
|Acquisition of new target (TT ref. 15.5 < R < 17.0)
|Acquisition of new target (TT ref. R>17.0)
|Dither with laser move
|Dither without laser move
|Recovery from aircraft or LTCS shuttering of the laser
- 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.
- 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.
- The observers should make a copy of their logs available to the
LGS-AO support team, to assist in the engineering analysis of the
- 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.
- 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.
- Authorship policies and suggested acknowledgments can be found