Beginning of the Night Cookbook for LUCIFER or MODS Observing

from the Telescope, Guiding and Active Optics perspective

Summary

Normal observers should only have to do the following at the beginning of the night. (See also the more detailed explanation below.)

  • Have a suitable on-axis guide/wfs star selected for the beginning of the night.
  • Preset to this star in TRACK mode, at PARALLACTIC angle 0.
  • Take a LUCIFER/MODS image. The OSA needs the XY offsets of the source to move the source to the rotator (pointing) center.
  • Have the OSA make a manual focus adjustment if the image is more than 5 arcsec in diameter.
  • When the OSA completes the pointing (IE/CA) and focus (Zglobal) corrections, preset to this same source as an on-axis WFS source in ACTIVE mode.
  • Allow WFS ~6 cycles to converge on the initial collimation.

At the bottom of the page there are descriptions of the sequence of events during TRACK, GUIDE, and ACTIVE mode observations.

Details

Startup on Instrument Operator's Workstation

  1. Display the IIFGUI for Telescope overall status information
  2. Display the GCSGUI to see the guider and WFS images

1 Display the IIFGUI for Telescope overall status information

Login to one of the workstations (obs1, obs2, obs3, obs4). Display the IIFGUI so the observer can see telescope status. The IIFGUI displays instrument authorization, mount status, rotator status, primary, secondary and tertiary mirror status, and guiding status. This display is most useful for following the status of your preset while it is in progress. As of March 2009, the IIFGUI has a new line that displays what the IIF sequencer is waiting on during a preset.

  • % IIFGUI &

2 Display the GCSGUI to see the guider, acquisition and WFS images

  • % GSCGUI &

As of 13-Sep-2008, the GCSGUI image display works (and is faster than the Guider.py script) , but all the other status information on GCSGUI may not be implemented.

Beginning of the Night Activities in greater detail

  • Have a suitable on-axis guide/wfs star selected for the beginning of the night.

  • Preset to this star in TRACK mode, at PARALLACTIC angle 0.
    • Positions telescope (azimuth, elevation, rotator)
    • Collimates mirrors (m1, m2 and m3)
    • Parks the AGw probe since we are not guiding

  • Take a LUCIFER/MODS image. The OSA needs the XY offsets of the source to move the source to the rotator (pointing) center. (These instructions are still correct but obsolete as now there is a LUCIFER script to do this.)
    • Alternately, this image can be taken with the AGw probe positioned on-axis by presetting in ACQUIRE mode.
    • The OSA will adjust PCS parameters IE (elevation arcsec) and CA (azimuth arcsec) with ptmodify to center the star. These numbers are adjustments to the Pointing Model zeropoints, and need to be re-entered if PCS is restarted. The corrections should only be large (more than 10-15 arcsec) if there is a significant thermal gradient in the telescope structure.
      • Marco has a program that does this calculation if you don't want to do it iteratively. See /home/mpedani/Pointing/PointadjustLUCI.
    • It may be necessary to repeat the pointing correction once or twice during the night depending on varying temperature conditions.
  • Have the OSA make a manual focus adjustment (M1 Zglobal) if the image is more than 5 arcsec in diameter. The amount of this correction (typically +0.2 to +0.4 mm) depends on the amount of heating of the telescope windbracing structure during the day.

  • When the OSA completes the pointing (IE/CA) and focus (Zglobal) corrections, preset to this same source as an on-axis WFS source in ACTIVE mode.
    • Allow WFS ~6 cycles to converge on the initial collimation.
    • If initial collimation is much worse than about 4 arcsec image quality, send manual corrections to PSF M1 to roughly collimate and focus.
    • Once this initial collimation for the night is achieved, it may be useful to manually add them to the PSF Global Offsets buffer so that they are preserved when PSF Clear Active Optics is performed during the night.

Observing Activities

Open-loop Tracking

  • Preset to a star in "TRACK" mode
    • Positions telescope (azimuth, elevation, rotator)
    • Collimates mirrors (m1, m2 and m3)
    • Parks the AGw probe out of the LUCIFER field
    • Returns success

Guiding

  • Preset to a star in "GUIDE" mode and specifying guide star coordinates
    • Positions telescope (azimuth, elevation, rotator)
    • Collimates mirrors (m1, m2 and m3)
    • Positions AGw probe on the guide star
    • Takes an acquisition image on guider camera
    • Offsets telescope to position the guide star on WFS hotspot
    • Returns success after two good guider images
    • Continues taking guide exposures and adjusting telescope tracking

  • To stop guiding, send a new preset in "TRACK" (or other) mode.
    • To stop guiding, and leave telescope tracking at the same position, issue the GCS stopGuiding command. However, beware that this stops guiding in GCS only - leaving IIF/CSQ thinking that the telescope is still in "Guide" mode. (This will stop you from sending offset commands)

  • To pause / resume guiding (on the same field), use the GCS pauseGuiding and resumeGuiding commands (not yet available on the GCSGUI).

Active Optics

  • Preset to a star in "ACTIVE" mode and specifying guide star coordinates
    • Positions telescope (azimuth, elevation, rotator)
    • Collimates mirrors (m1, m2 and m3)
    • Positions AGw probe on the guide star
    • Takes a acquisition image on guider camera
    • Offsets telescope to position the guide star on WFS hotspot
    • Returns success after one good guider images
    • Continues taking guide exposures and adjusting telescope tracking
    • Starts loop of taking wavefront measurements

PSF Defaults for Active Mode

  • Send corrections to "Split" (Means focus and coma to fixed M2, and other Zernikes to M1.) (Formerly named "Default")
  • Do not "Hold WFS Corrections". (If corrections are held, no active optics corrections are applied until a stepFocus command is issued.) Setting "Hold WFS Corrections" to Yes allows you to take images between 70 and 180 sec without any active corrections being applied during the integration.
  • Always "Offload" the active optics corrections on M2 whenever a stepFocus command is issued. As of 6-Jan-2009, this should automatically adjust for any M1 Collimation table updates that are needed at the time of the offload.
  • Leave "OSS Sphere" mode set to No.

More details on these PSF arbitrator controls can be found on the ActiveOpticsModes page.

Acquisition with the guide camera

  • Preset to a star in "ACQUIRE" mode at PARALLACTIC angle 0, and specifying guide star coordinates
    • Positions telescope (azimuth, elevation, rotator)
    • Collimates mirrors (m1, m2 and m3)
    • Positions AGw probe on the guide star
    • Starts a movie mode of full-frame guide camera images displayed on the GCSGUI
    • Returns success

Troubleshooting

If No Guide Star for LUCIFER

  • Check weather (clouds?)
  • Check telescope mount (MCSPU) in "Tracking" mode and "On-source"
  • Check that IIF Preset state is in "GUIDE" or "ACTIVE" mode
  • Check Preset and Guidestar Coordinates
  • Check AGw probe position
  • Check Pointing Model zeropoints
  • Check Primary Mirror collimation status
  • Check Secondary Mirror collimation status.
  • Check Tertiary Mirror collimation status
  • Check if LUCIFER calibration unit is deployed
  • Check cover on Secondary Mirror
  • Check cover on Tertiary Mirror
  • Check dust cover on AGw unit
  • Check swing arm positions
  • Check shutter doors
  • Is GCS talking to the correct AGW unit?
  • Is GCS talking to the correct AzCam inside the AGW?

If No Guide Star for MODS

  • Check weather (clouds?)
  • Check telescope mount (MCSPU) in "Tracking" mode and "On-source"
  • Check that IIF Preset state is in "GUIDE" or "ACTIVE" mode
  • Check Preset and Guidestar Coordinates
  • Check AGw probe position
  • Check Pointing Model zeropoints
  • Check Primary Mirror collimation status
  • Check Secondary Mirror collimation status.
  • Check if MODS internal cover is closed
  • Check cover on Secondary Mirror
  • Check swing arm positions, especially M3 swing arm retracted
  • Check shutter doors
  • Is GCS talking to the correct AGW unit?
  • Is GCS talking to the correct AzCam inside the AGW?

John's Special Instructions for Adjusting the Azimuth Zeropoint when there are pointing problems - 11-January-2010

These "special" pointing problems seen on 20100108 UT seem to be caused by a change in the Azimuth Zeropoint on the timescale of a day or so. Here are the instructions needed to work around the problem. (version 2, updated 11-Jan-2010) This problem was solved in April 2010, so the 2-star pointing correction is no longer needed..

  • Verify with the TO that he has checked and/or reset the encoders at AZ=120 EL=90.
  • Do a ptreset to be sure you have the default pointing model for LUCIFER.
  • It may save time to restore the value of IA from the previous night if it was significantly different from the default.

  • Preset to a pointing star at high elevation (70-80 degrees EL) on the meridian in TRACK and PARALLACTIC modes. (This position is relatively less sensitive to IA as COS(EL).)
  • Measure the position of the star and adjust IE and CA as you normally would.

  • Preset to a pointing star at low elevation (15-25 degrees EL) on the meridian (160-200 degrees AZ) in TRACK and PARALLACTIC modes.
  • Measure the position of the star as if you were going to adjust IE and CA. But have the TO apply these corrections to IE and IA (not CA) with ptmodify.

  • If your IA adjustment at low elevation was more than 30 arcsec, then you should iterate with another star (or the same star) at high elevation to make a refinement of CA.

At this point you can proceed with normal observing. Big (arcminute) pointing corrections should not be needed, but you still might want to make Small (< 10 arcsec) pointing corrections with a pointing star near your target.

Note: In case you stop to admire the extrafocal pupil, or get distracted by something else while adjusting IE/CA/IA, be sure to update M1 collimation if you've taken more than a few minutes since the last collimation.

-- JohnHill - 07 Sep 2008
Topic revision: r20 - 26 Sep 2010, JohnHill
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