Science Operations

MOS Spectroscopy

Note: Please do not leave the mask in turnout for long periods! Motor current is used to hold the mask in this position and over time it will warm up parts of LUCI.

Spectroscopy (both Longslit and MOS) scripts are comprised of an acquisition component and science component.

MOS Acquisitions

  1. “Load” the Observing Script into the Observation Execution GUI.
  2. Once the script has been loaded into the Observation Execution GUI, confirm with the OSA that it is safe to slew to the target
  3. Select the “GO!”  Queue Action Button. This will send the telescope preset and instrument configuration. The filters, camera, etc. will move into place as the telescope slews into position.  Once in position, the predetermined guide star will be acquired by GCS.

    The telescope will collimate, and once the wavefront sensor error WFE (circled above in the GCS GUI) is below ~800 nm, LUCI will proceed with executing the observations. 
  4. The first obsitem will be a sky image.  This is an image offset from source nominal position.  The second obsitem will be the source taken at the original position.  The third is a mask through slit image.
  5. The MOS mask alignment:
    1. Select the MOS tab in the RTD GUI.
    2. Confirm the auto-populated filename in the slit selection section is correct, then click “Use”.
    3. Select a SlitID number (SlitID with the pulldown) for reference slit 1, then in the Aladin display, click on that reference slit in the image. Do the same for at least reference slit 6.  You can zoom and click multiple times to get reasonably close to centered on your target. Repeat for at least a second reference slit.
    4. Click “Set Position” and confirm that the shifts look reasonable. The rotation on LUCI2 is typically a bit under 0.5 degrees.
  6.  MOS target alignment:
    1. In the Target Alignment portion of the Longslit tab of the RTD GUI, confirm the auto-populated filenames for alignment (source) and background (sky) are correct, then click “Subtract images”. Or if on a bright source and no sky image was taken, ensure the filename for the source is populated and select “Single img…”.
    2. Set a reference target ID number, then in the Aladdin display click on that reference source in the image. You can zoom and click multiple times to get reasonably close to centered on your target.
    3. Click Set position to centroid on this source.
    4. Click “Calculate”  in the MOS tab. This will auto-find the remaining alignment sources and then calculate the affine transform to align the mask to the sky
    5. In the “target offsets” section at the bottom of the MOS tab on the RTD, check if any of the alignment sources have large residuals on the fit. If so, uncheck its “use” box and click calculate again. If all seem off, select a second source and repeat the previous four steps.  If one source has particularly large, you may wish to deselect this one source as it is possible that the astrometry on this source is bad.  Recalculate and check residuals.
  7. Once confirmed that the offsets make sense (the residuals are not too large), then send. This will insert an offset ObsItem into the queue.
  8. Click “Go!” on the Observation Execution GUI. This will execute the alignment offset, take the source+mos mask image and then pause the queue.
  9. If you are happy with the source alignment on the slit, click “GO!” again to start executing the spectroscopic portion of the script. If not, you may manually execute a small offset on the Telescope Service GUI and take another image to confirm your source position in the slit.  Manually take the other image using the RMGUI.