LWS
Observing Checklist

The following procedures describe the acquisition of new targets in the two basic observing modes.

Summary

Target Acquisition: Imaging Mode

Follow these steps to acquire a new target in direct imaging mode.
  1. Stop image collection.
    Wait for the exposure in progress to complete, or follow these steps to interrupt an exposure in progress:
    • Halt data acquisition by clicking Abort on the XPOSE/LWS widget.
    • Return the telescope to the on-source nod beam by typing the following command in the keokea window: 
      md nodtel=off

  2. Halt chopper.
    Stop the chopper by clicking Stop on the Chop Nod Control window.

  3. Move to new target.
    When ready to move, let the OA know the name of your next target and the sky position angle you require for the observations. The OA will preview the target using the telescope control software to select a nearby catalog star that will be used to verify pointing upon arrival at your target coordinates. In a few moments, the telescope will start to slew.

  4. Configure spectrograph.
    If changes to the LWS settings are required (different filters, gratings, etc.), then it is most efficient to make the changes during a slew.

  5. Receive target on guider.
    After establishing that the pointing is correct, the OA will generally place the target onto the guider. If you expect your target to be visible in the guider (i.e., R<20) then ask the OA to put your target on the guider, center it up, and send it to LWS. Otherwise, simply ask the OA to send your target to LWS. Then wait while the OA selects a guide star and begins guiding.

  6. Reset chop and nod parameters.
    To set the nod direction and throw for chop-nod mode, follow these steps:
    • In the Chop Nod Control window, enter your desired chop amplitude in the Chop Amplitude box. Values from 0 to 50 arcsec are legal; a typical value for imaging is 10 arcsec (the size of the LWS field of view).
    • Enter the desired chop angle in the Chop Angle box. For north-south chopping, enter 0. For chopping parallel to detector columns, enter the current sky position angle (as displayed on FACSUM) here.
    • Click on the Start button to begin chopping.

  7. Take initial image of target.
    1. In XPOSE/LWS, click Set Mode to bring up the mode menu.
    2. Click Video to select video mode.
    3. A window will appear warning you that the chopper is not engaged. Click on Acquire w/ Chop to start the chopper.
    In about 15 seconds, QuickView should display the image.

  8. Center target on LWS.
    • In Quickview, click the droplist at top left and select Buffer Control.
    • Click on Non-accumulate to disable co-adding of frames during acquisition.
    • Click on Chop Difference to view the difference of chop beams.
    • When a decent image of the source is visible, click Static Mode to grab the image.
    • Click the droplist at top left and select Move Tel... to call up the move telescope menu.
    • Click From to set the source position.
    • If the target is a point source and is easily visible on the image, click Centroid to measure a centroid, then move the mouse onto the image of the object and click left mouse to trigger the centroid measurement. The measured centroid coordinates will appear in the boxes labeled From X and From Y.
    • If the target is only barely visible or not a point source, click Cursor XY, move the cursor onto the approximate image center and click left mouse. The coordinates of your mouse click will appear in the boxes labeled From X and From Y.
    • Click To Center to set the destination to be the image center.
    • Click Move Telescope to send the object to the center of the field. This will take about 5-10 seconds.
    • On the droplist at top left, select Buffer Control.
    • On the Buffer Control menu, click Dynamic Mode to re-enable updates.
    • Wait for the Quickview image to update, and apply additional corrections as needed until centering is achieved.

  9. Begin data acquisition.
    In XPOSE/LWS:
    • Click on Abort to halt data-taking.
    • Click Set Mode to bring up the mode menu.
    • Click Imaging to select imaging mode.
    • Enter the desired on-target integration time in the ObjTime entry box.
    • Click on GO to resume data-taking.
    • Verify that the upper boxes on Xpose/LWS read Acquiring and Recording.
    The system will acquire a single image; click GO again to take more images if desired.

Target Acquisition: Spectroscopy Mode

Follow these steps to acquire a new target in spectroscopy mode.
  1. Stop image collection.
    Wait for the exposure in progress to complete, or follow these steps to interrupt an exposure in progress:
    • Halt data acquisition by clicking Abort on the XPOSE/LWS widget.
    • Return the telescope to the on-source nod beam by typing the following command in the keokea window: 
      md nodtel=off

  2. Halt chopper.
    Stop the chopper by clicking Stop on the Chop Nod Control window.

  3. Move to new target.
    When ready to move, let the OA know the name of your next target and the sky position angle you require for the observations. The OA will preview the target using the telescope control software to select a nearby catalog star that will be used to verify pointing upon arrival at your target coordinates. In a few moments, the telescope will start to slew.

  4. Configure spectrograph.
    Take the following actions in the XLWS window:
    • In the Aperture area, click on OPEN and SET.
    • In the Grating area, click on MIRROR and SET.
    • In the Filter area, select the blocking filter to be used for your spectroscopy. and click SET.

  5. Receive target on guider.
    After establishing that the pointing is correct, the OA will generally place the target onto the guider. If you expect your target to be visible in the guider (i.e., R<20) then ask the OA to put your target on the guider, center it up, and send it to LWS. Otherwise, simply ask the OA to send your target to LWS. Then wait while the OA sets up on a guide star and begins guiding.

  6. Reset chop and nod parameters.
    To set the nod direction and throw for chop-nod mode, follow these steps:
    • In the Chop Nod Control window, enter your desired chop amplitude in the Chop Amplitude box. Values from 0 to 50 arcsec are legal; a typical value for imaging is 10 arcsec (the size of the LWS field of view).
    • Enter the desired chop angle in the Chop Angle box. For north-south chopping, enter 0. For chopping parallel to detector columns, enter the current sky position angle (as displayed on FACSUM) here.
    • Click on the Start button to begin chopping.

  7. Take initial image of target.
    1. In XPOSE/LWS, click Set Mode to bring up the mode menu.
    2. Click Video to select video mode.
    3. A window will appear warning you that the chopper is not engaged. Click on Acquire w/ Chop to start the chopper.
    In about 15 seconds, QuickView should display the image.

  8. Center target on on slit.
    Determine the object and slit centroids using Quickview:
    • In QuickView, click the droplist at top left and select Slit Align.
    • Click Chp-diff to display the differenced frame.
    • Click Object to set the source position.
    • If the target is a point source and is easily visible on the image, click Centroid to measure a centroid, then move the mouse onto the image of the object and click left mouse to trigger the centroid measurement. The measured centroid coordinates will appear in the boxes labeled Obj X and Obj Y.
    • If the target is only barely visible or not a point source, click Cursor XY to enable manual centroiding, move the cursor onto the approximate image center and click left mouse. The coordinates of your mouse click will appear in the boxes labeled Obj X and Obj Y.
    • In XLWS, select the desired slit and click Set to move that slit into the beam. Wait for the move to complete.
    • In QuickView, click Raw DC to display an undifferenced frame. An image of the slit should appear.
    • Click and drag middle mouse across the slit to define the destination. The slit centroid will be measured and copied into the boxes labeled Slit X and Slit Y.
    • When both source and destination coordinates are defined, click Move Telescope to send the offset. The message box will tell you when the move is completed.
    • Click Chp-diff to display the chop difference.
    • If the source is well centered, proceed to the next phase. If not well centered, remove the slit and re-run this centroiding procedure.

  9. Reconfigure Spectrograph.
    In XLWS:
    • Ensure that the proper slit is installed. Note that the two slits do not have the same center, and hence that you must use the same slit for spectroscopy as you have used for alignment.
    • Insert the desired grating (LRES or HRES.
    • Insert the desired blocking filter (generally N wide for spectroscopy near 10 µm or spec20 near 20 µm).

  10. Begin data acquisition.
    In XPOSE/LWS:
    • Click on Abort to halt data-taking.
    • Click Set Mode to bring up the mode menu.
    • Click LRES or HRES to select the appropriate detector parameters for your chosen spectroscopy mode.
    • Enter the desired on-target integration time in the ObjTime entry box.
    • Click on GO to resume data-taking.
    • Verify that the upper boxes on Xpose/LWS read Acquiring and Recording.
    The system will acquire a single image; click GO again to take more images if desired.

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Last modified: Sat Sep 6 23:51:16 HST 2003