DEIMOS Slitmask Alignment Checklist

Purpose

This checklist describes the procedure for aligning multiobject slitmasks on DEIMOS, assuming you are:

using slitmasks which have alignment boxes
using the xbox software for slitmask alignment

Procedure

The DEIMOS development team at UCO/Lick has delivered a sophisticated and highly automated slitmask alignment software package which makes the procedure relatively quick and painless. In order for the automated procedure to succeed at night, it is necessary for the observer to perform some rudimentary calibration procedures in the afternoon.

Afternoon Calibration

The goal of this procedure is to tune parameters of the optical modeling algorithm in order to get the correct mapping from physical position on the slitmask to CCD pixels. Only one DEIMOS image must be acquired to complete the calibration.

Select alignment mode. Determine the spectrograph configuration which will be used for slitmask alignment imaging. Options are:
- Zeroth order imaging. This is the preferred option, since moving the grating to the zeroth order position is much faster than switching to the mirror. This method may not work well if the alignment stars are very faint (R > 20).
- Mirror imaging. This is the fallback option if the alignment stars are very faint, or if seeing/transparency conditions are poor.
Configure DEIMOS. Insert the slider which will be used for imaging your masks. (Note: while it's not necessary to use a single slider for all of your slitmask alignment imaging, doing so will simplify the process; we assume the one-slider case here.) For zeroth order imaging, the steps are:
- Open the Gratings Panel by double-clicking on the Grating box on the main Dashboard GUI.
- At the left-hand side of the Gratings Panel, click on the name of the grating you will use with this slitmask to move it into position.
- Once the grating is in position, click on the GO ZERO button at the right-hand side of the GUI to move the grating to the imaging position.
For the mirror, simply select Mirror from the Grating box on the main dashboard GUI.
Acquire slitmask images. Obtain direct images of all of your slitmasks so that you can verify them and calibrate xbox:
1. Configure the spectrograph with your primary grating for the night.
2. From the DEIMOS Workspace Menu, select DEIMOS Utilities > Slitmask Imaging Toool to launch the widget.
3. Select all masks to be observed using this grating.
4. Click GO to acquire direct images of the masks.
5. If the secondary slider will also be used, insert this slider, select the masks to be observed with it, and click GO to acquire images with the other slider.
Configure xbox. In this step, you will tune the parameters of the DEIMOS optical model so that the software can predict the pixel location of your alignment boxes based on the information in the slitmask design file.
1. From the instrument menu, select IRAF/IDL --> cl ds9 (IRAF)
2. Run IRAF and an associated ds9 window by typing xiraf and load packages keck and deimos.
3. In IRAF, execute the command cdata to take you to the current data directory.
4. Next, issue the command
```
	tune_qmodel image
```
  where image is the name of your alignment image. The program will display the alignment image on ds9 and mark the (inaccurate) predicted locations for the alignment boxes in red.
5. When prompted by the software, place the cursor in the exact center of any one of the alignment boxes on the image display and press any key. The program will then adjust the qmodel parameters mu and roll3 in order to achieve agreement between the predicted and indicated positions for this alignment box. The resulting locations of all alignment boxes will then be marked on the image in green.
6. The script will now run xbox for you in practice mode. Verify that all of the alignment boxes on the displayed image are properly found. If so, then the optical model is properly tuned and xbox is ready for action.
7. Verify masks. Run xbox in practice mode on all of your slitmasks to verify that the masks were cut correctly and that the software predicts the correct box location in each case. If it fails on certain masks, use the check_boxes command in IRAF to show where xbox is looking for boxes and try to determine why they are not being found. Likely reasons are:
  - Box falls in the gap between two CCDs.
  - Box lies on a bad column.
  - Box was placed too close to the edge of the field of view and was removed.
  - The information on slitmask design in the image header is corrupted.
For problem masks, use check_boxes to generate a file of box positions and feed this as an input file to xbox.

Return to the Afternoon Checklist.

Nighttime Observing Procedure

Focus telescope.
- Tell the OA the name of your target as listed in your starlist file and also the position angle for the instrument rotator.
- To save time, configure the instrument to run Mira while the telescope is slewing:
  - Set hatch to OPEN
  - Set slitmask to None
  - Set grating to:
    - slider 3 or 4 if you plan to align using the grating for imaging (remember to set to zeroth order imaging position by pressing the GO ZERO button), or
    - to mirror if you plan to align using the mirror for imaging
  - Set filter to R
- Ask to OA to run Mira in the neighborhood of your target.
- Wait about 10 minutes for the OA to acquire an appropriate star and run Mira.
Acquire target.
When the OA tells you that your target is on DEIMOS, check the following information on FACSUM to verify that your position is correct:
- Target name and coordinates
- Pointing origin (should be DEIMOS)
- Position angle (skypa on FACSUM). Note: also verify that the rotator is not rotating into a limit by checking the rotator screen on the dashboard.
Complete rough alignment.
The goal of this step is to put the alignment stars into their boxes. Ideally it will be completed the easy way by positioning a star to a given position on the guider; failing that, it will be completed the hard way by taking an image on the science detector.
- The Easy Way.
  One of the pieces of information output by the Lick-supplied slitmask design software is the desired coordinate at which you should place a fiducial star in order to get the slitmask coarsely aligned. To do so:
  - Identify the fiducial star on the guider image.
  - Place the cursor on the star and note the current (x,y) coordinates.
  - At a polo prompt, use the gmov command to perform a telescope offset from the current coordinates (x1,y1) to the desired coordinates (x2,y2):
```
	gmov x1 y1 x2 y2
```
- The Hard Way.
  If the Easy Way fails to work, you can try this alternative method:
  - Configure the instrument for imaging:
    - select slider 3 and set to zeroth order imaging position, or insert mirror
    - set slitmask to None
    - set CCD readout mode to Direct
    - set exposure time to 20 sec
  - Acquire first exposure.
  - Insert the appropriate slitmask.
  - Acquire second exposure.
  - Using FIGDISP or IRAF, identify one alignment star on the first image and measure the pixel coordinates. Call these x1 and y1.
  - On the second image, identify the corresponding alignment box for the alignment star and note the coordinates of the box center. Call these x2 and y2.
  - Move the telescope by typing the following command into a polo window:
```
	mov x1 y1 x2 y2
```
    The alignment stars should now be in their boxes; proceed with fine alignment.
Complete fine alignment.
In this step, you will refine the positions of the stars within their respective alignment boxes to achieve optimal centering of the slitmask.
- Have the OA select a guide star and begin guiding. Ensure that the guide star selected is not too close to the edge of the guider field, since small offsets may still be required.
- Start a 20-40 sec direct exposure through the slitmask.
- In your IRAF window, type do_xbox anytime before the image has been written to disk. The script will wait for the current image to be written, will determine the name of the image, and then will beep to indicate that it's time for you to wake up and run xbox.
- To run xbox on your image:
  - For each alignment box, xbox will plot row and column cuts through the box to show the quality of the centering. Press:
    - q if the centering is acceptable
    - i to ignore the current box if the star is not seen or the object is inappropriate (bad coordinates, galaxy, double-star, etc.)
    - spacebar to reset the sky level if it was incorrectly measured by the program (sky will be reset to the current y-position of the cursor)
  - When done reviewing all boxes, xbox will plot a residual map. If any discrepant points are noted, press d to delete the offending point and f to re-do the fit. Press q when the fit is acceptable.
  - The program will report the suggested moves in rotation and position, as well as the uncertainties (in parenthesis).
  - Answer y to the prompt:
```
     [CONFIRM]  Send DCS commands? (y/n) [y]:
```
  - Accept the suggested rotator move if it is significant compared to the uncertainty.
  - Perform another alignment iteration if:
    - a rotator move was required, or
    - either the north or east offset was > 0.2 arcsec (or whatever your personal tolerance is)
Set up for spectroscopy.
- Reconfigure the instrument for spectroscopy:
  - Set grating to the appropriate central wavelength (if using zeroth order imaging you can use the GO BACK button to return to original setting).
  - Set filter to the desired position for order blocking.
  - Set dewar focus as appropriate for the selected filter.
- Set the detector parameters appropriately:
  - Set ReadOut to Spectral.
  - Set ObsType to Object.
  - Set ExpTime as desired for spectroscopy.
Wait for FCS to settle. Do not start your exposure until the FCS GUI shows the FCS status as locked, or it may be smeared.
Expose!

Purpose

Procedure

Afternoon Calibration

Nighttime Observing Procedure

See Also