Summary

This web page describes how to align a DEIMOS longslit on a science target when the image of the target is not visible on the DEIMOS guider. The Observing Assistant can easily align targets that are visible on the guider with the slit.

Procedure

Slew to the target.
Set the rotator angle as desired.
Configure for imaging.
Prepare DEIMOS for direct imaging:
- Insert desired imaging filter (e.g., R).
- Either:
  - Send the grating to the zeroth order imaging position via the GO ZERO button on the grating subpanel, or
  - Insert the imaging mirror (switch to slider 2)
Image the longslit.
- Select the appropriate longslit mask.
- Select Direct readout mode on CCD system.
- Select Object image type on CCD system.
- Select appropriate exposure time (e.g., 30 sec).
- Acquire an image.
Determine destination coordinates.
Inspect the mask image on ds9 and note the PANE coordinates of the slit center. If you are unsure about the horizontal position to choose, then:
- Ask the Observing Assistant to center a star in your preferred slit.
- Acquire a direct image.
- Measure the pixel coordinates of the star center.
Call these coordinates Xslit and Yslit.
Center star at slit location.
- Ask the OA to point the appropriate longslit to your target coordinates.
- Remove the longslit by setting the slitmask to None.
Offset telescope to center star at slit location.
- Acquire an image sufficiently long to reveal your target. Typical exposure times are 30-60 sec.
- Identify your target on the ds9 image display.
- Note the PANE coordinates of your target. Call these coordinates Xsstar and Ystar.
- Issue the command
```
	mov Xstar Ystar Xslit Yslit
```
  substituting appropriate values for Xstar, Ystar, Xslit, and Yslit.
Confirm move (optional).
If desired, repeat the previous step to confirm that the target is at Xslit and Yslit.
Acquire science images.
- Insert the desired longslit.
- Return grating to science wavelength (use GO BACK if you used GO ZERO previously.
- Reset filter to appropriate spectroscopy blocker.
- Reset CCD parameters:
  - Readout to Spectral
  - Exposure time to an appropriate value.
- Wait for FCS to track.
- Expose.

Note

Because flexure compensation is not applied in direct imaging mode and the grating may not always complete tilt moves, you must re-measure the slit coordinates (Xslit and Yslit) for each new target rather than assuming that the previous values apply.