The OSIRIS spectrometer fields of view are relatively small (as small as 0.32 x 1.25 arcsec) and not necessarily concentric, thus a precise target acquisition is crucial to most observing programs. Pointing with the AO system is accurate once the system is locked on a tip-tilt star although the NGS system is not quite as good as the LGS system. NGS errors in offsetting can be as great as 0.050 arcsec where the LGS offsetting errors are less then 0.010 arcsec. Following the steps below will help ensure that your object is located on the lenslet array. The procedures below refer to "modes" of the instrument which are defined as filter/scale combinations. There are 88 different modes for OSIRIS.

Procedures:
  1. LGSAO Direct Acquisition on Spectrometer
  2. LGSAO Acquisition on Spectrometer using OSIRIS Imager for Acquisition Only
  3. LGSAO Acquisition on Spectrometer using OSIRIS Imager for Science Images and Acquisition
  4. NGSAO Direct Acquisition to Spectrometer
  5. NGSAO Acquisition on Spectrometer using OSIRIS Imager for Acquisition and/or Science


  1. LGSAO Direct offset from Guide star to Science object:
  2. The fastest and most accurate acquisition is a direct offset from guide star to science object, assuming precise offsets have been determined.

    1. Starlist
    2. Prior to observing night, enter precise relative coordinates in the Keck starlist for both the guide star and science target.
      Note: The guide star should include a B-V or B-R color to minimize the effects of differential atmospheric refraction (DAR) between the visual wavelength tip-tilt control and infrared science instrument. If precise relative astrometry is not available for your tip-tilt star / science target, you may need to use the imager acquisition procedure below.
    3. Record OSPEC pointing coordinates
    4. Record the OSIRIS spaxel (sometimes referred to as lenslet or spectrometer pixel) coordinates for the OSPEC pointing origin in Kn3-0.020 arcsec scale, This is only needed once per night and is typically done during the lgsao checkout or on the first tip-tilt star.
      Note: If the tip-tilt star color is not supplied, check the tip-tilt star alignment on the spectrometer before offsetting to the science object if precise pointing is required.
    5. Slew to target
    6. Ask OA to slew to tip-tilt star, pointing origin: OSPEC .
    7. Set Rotator
    8. Use the Rotate tab of OSIRIS telescope GUI (OTGUI) to set the sky rotator angle (position angle mode).
      Note: vertical angle mode can only be used when the science object is its own tip-tilt star (sometimes referred to as "on-axis" observations)
    9. Close loops
    10. LGSAO operator performs Tip-Tilt and Laser acquisition; DAR set to acquisition and track.
    11. Center tip/tilt star
    12. Using the "Offset" tab of OSIRIS telescope GUI (OTGUI), enter the spaxel coordinates recorded in step 2 with Kn3-0.020 as the "from" selection. Enter the "Center of" and OSIRIS mode of your choice as the "to" selection of the offset tool and click the "GO" button associated with the From-To feature.


    13. Optional: Integrate on tip/tilt star
    14. Take an OSIRIS spectrometer dataset on the Tip-Tilt star to confirm accurate centering and/or sample the on-axis PSF.
    15. Offset to target
    16. Instruct LGSAO operator to offset to target and wait for AO system to settle.
    17. Integrate on science target
    18. The science target should be well centered on the OSIRIS field of view and ready for science integrations.
    19. Re-center
    20. To center-up in other modes of OSIRIS, it is important to use the offset tool prior to each mode change since the various modes are not necessarily concentric. Use the "center of" feature in both the "From" and "To" fields of the offset tab.
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  3. LGSAO, Using the OSIRIS Imager as an acquisition tool only.
  4. Note: The following procedure maintains the laser pointing on OSPEC and thus the Imager data will not necessarily be of the highest quality.

    1. Slew to target
    2. Ask OA to slew to tip-tilt star, pointing origin: OSPEC.
    3. Set Rotator
    4. Use the Rotate tab of OSIRIS telescope GUI (OTGUI) to set the sky rotator angle (position angle mode).
      Note: vertical angle mode can only be used when the science object is its own tip-tilt star (sometimes referred to as "on-axis" observations).
    5. Close loops
    6. LGSAO operator performs Tip-Tilt and Laser acquisition; DAR set to acquisition and track.
    7. Offset to target
    8. Instruct LGSAO operator to offset to target and wait for AO system to settle.
    9. Offset to Imager
    10. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI) to offset from center of Kn3-0.020 to center of Imager.
    11. Record Imager pixel
    12. Acquire image data and record pixel coordinates of science object.
    13. Offset to center of Spectrometer
    14. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI) , offset from Imager pixel (recorded in previous step) to center of the OSIRIS mode of your choice (example: Spec 0.035 arcsec Kbb).
    15. Integrate on science target
    16. The science target should be well centered on the OSIRIS spectrometer field of view and ready for science integrations.
    17. Re-center
    18. To center-up in other modes of OSIRIS, it is important to use the offset tool prior to each mode change since the various modes are not necessarily concentric. Use the "center of" feature in both the "From" and "To" fields of the offset tab.

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  5. LGSAO, Using the OSIRIS Imager to obtain high strehl image data and as an acquisition tool:
    1. Slew to target
    2. Ask OA to slew to the tip-tilt star, pointing origin: OSPEC.
    3. Set Rotator
    4. Use the Rotate tab of OSIRIS telescope GUI (OTGUI) to set the sky rotator angle (position angle mode).
      Note: vertical angle mode can only be used when the science object is its own tip-tilt star (sometimes referred to as "on-axis" observations)
    5. Close loops
    6. LGSAO operator performs Tip-Tilt and Laser acquisition ; DAR set to acquisition and track
    7. Offset to target
    8. Instruct LGSAO operator to offset to target and wait for AO system to settle.
    9. Set Laser=1
    10. Instruct LGSAO operator to set the laser = 1 flag. This puts the laser steering in slave mode and thus will be pointed to the imager field when the object is offset to the imager.
    11. Two step offset to Imager
    12. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI), to offset from the spectrometer to the imager. This step must be performed in two steps to avoid an AO fault (FSM). Offset in Spec X/Y arcsec, [7.0, -7.0] and [8.14, -7.39] for a total of [15.14, -14.39]. See example below.

    13. Integrate on Imager, record pixel
    14. Acquire image data and record pixel coordinates of science object.
    15. Center on Imager
    16. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI), offset from Imager pixel (recorded in previous step) to center of the Imager.
    17. Two step offset to Spectrometer
    18. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI), offset from Image center to OSPEC Kn3 0.020 arcsec center in two steps: Offset in Spec X/Y arcsec, [-7.0, 7.0] and [-8.14, 7.39] for a total of [-15.14, 14.39]
    19. Center on Spectrometer
    20. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI) , offset from center to OSPEC Kn3 0.020 arcsec to to center of the OSIRIS mode of your choice (example: Spec 0.035 arcsec Kbb).
    21. Integrate on science target
    22. The science target should be well centered on the OSIRIS spectrometer field of view and ready for science integrations.
    23. Re-center
    24. To center-up in other modes of OSIRIS, it is important to use the offset tool prior to each mode change since the various modes are not necessarily concentric. Use the "center of" feature in both the "From" and "To" fields of the offset tab.

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  6. NGSAO Direct offset from Guide star to Science object:
  7. The fastest and most accurate acquisition is a direct offset from guide star to science object, assuming accurate offsets are known.

    1. Slew to target
    2. Ask the OA to slew to the tip-tilt star, pointing origin: OSPEC ( or USER1 or USER2 if previously calibrated).
      Note: pointing should be calibrated each night using a bright star. If the OSPEC pointing origin is not centered in Kn3 0.020 arcsec field, ask the OA to define user position after centering a stare in the OSIRIS Kn3 0.020 arcsec field, .
    3. Set Rotator
    4. Use the Rotate tab of OSIRIS telescope GUI (OTGUI) to set the sky rotator angle (position angle mode).
      Note: vertical angle mode can only be used when the science object is its own tip-tilt star (sometimes referred to as "on-axis" observations)
    5. Close loops
    6. OA performs AO acquisition; DAR set to acquisition only
    7. Offset to target
    8. Offset to science target using the "Offset" tab of OSIRIS telescope GUI (OTGUI). If the move is greater than 10 arcsec radius, This step must be performed in two or more steps to avoid an AO fault (FSM). Offset in RA/Dec arcsec (en). Example [7.0, -7.0] and [8.0, -7.0] for a total of [15.0 -14.0].
      Note: The limits of FSM space can be viewed at the following links:
      FSM guide star ION tool
      AO guide star tool
    9. Center on Spectrometer
    10. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI), to offset from center to OSPEC Kn3 0.020 arcsec to the center of the OSIRIS mode of your choice (example: Spec 0.035 arcsec Kbb).
    11. Integrate on science target
    12. The science target should be well centered on the OSIRIS spectrometer field of view and ready for science integrations.
    13. Re-center
    14. To center-up in other modes of OSIRIS, it is important to use the offset tool prior to each mode change since the various modes are not necessarily concentric. Use the "center of" feature in both the "From" and "To" fields of the offset tab.

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  8. NGSAO, Using the OSIRIS Imager as an acquisition tool and/or to obtain high strehl image data:
    1. Slew to target
    2. Ask OA to slew to the tip-tilt star, pointing origin: OSPEC ( or USER1 or USER2 if previously calibrated)
      Note: pointing should be calibrated each night using a bright star. If the OSPEC pointing origin is not centered in Kn3 0.020 arcsec field, ask the OA to define user position after centering a stare in the OSIRIS Kn3 0.020 arcsec field .
    3. Set Rotator
    4. Use the Rotate tab of OSIRIS telescope GUI (OTGUI) to set the sky rotator angle (position angle mode).
      Note: vertical angle mode can only be used when the science object is its own tip-tilt star (sometimes referred to as "on-axis" observations)
    5. Close loops
    6. OA performs AO acquisition; DAR set to acquisition only
    7. Offset to target
    8. Offset to science target using the "Offset" tab of OSIRIS telescope GUI (OTGUI), Offset in RA/Dec arcsec (en).If the move is greater than 10 arcsec radius, This step must be performed in two or more steps to avoid an AO fault (FSM). Offset in RA/Dec arcsec (en). 
    9. Two step offset to Imager
    10. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI), to offset from the spectrometer to the imager. This step must be performed in two steps to avoid an AO fault (FSM). Offset in Spec X/Y arcsec, [7.0,-7.0] and [8.14, -7.39] for a total of [15.14, -14.39]. See example below:

      Note: In this case where two offsets are occurring, both from the guide star and to the imager, its is more likely to exceed the FSM limits: Double check the guide star limits in FSM space for both pointings (imager and spectrometer) at one of the following links:
      FSM guide star ION tool
      AO guide star tool
    11. Record Imager pixel
    12. Acquire image data and record pixel coordinates of science object.
    13. Center on Imager
    14. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI) , offset from Imager pixel (recorded in previous step) to center of the Imager.
    15. Two step offset to Spectrometer
    16. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI) , offset from Image center to OSPEC Kn3 0.020 arcsec center in two steps: Offset in Spec X/Y arcsec, [-7.0, 7.0] and [-8.14, 7.39] for a total of [-15.14, 14.39]
    17. Center on Spectrometer
    18. Use the "Offset" tab of OSIRIS telescope GUI (OTGUI) , offset from Center of OSPEC Kn3 0.020 arcsec to to center of the OSIRIS mode of your choice (example: Spec 0.035 arcsec Kbb).
    19. Integrate on science target
    20. The science target should be well centered on the OSIRIS spectrometer field of view and ready for science integrations.
    21. Re-Center
    22. To center-up in other modes of OSIRIS, it is important to use the offset tool prior to each mode change since the various modes are not necessarily concentric. Use the "center of" feature in both the "From" and "To" fields of the offset tab.

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