User`s guide

FLAMINGOS at the MMT
B. Mosplate Alignment
1. Load the mask design image and region file into buffer 3 of ds9. Flip and rotate until the image's WCS
matches that of a raw Flamingos frame. Turn on tiling, with a vertical orientation.
2. Acquire target on Flamingos and attempt to visually pick out the alignment targets (stars or galaxies). If
necessary, adjust telescope pointing with relative.offset.mmt.pl until the targets are within the central
region of the array. If targets are faint, may need to offset a small amount and work on a difference
image.
3. Have the telescope operator acquire a guide star and start guiding.
4. Have the telescope operator adjust focus on the guide camera, then check focus on Flamingos and tweak
if necessary.
5. Insert the decker mos baffle using config.filter.grism.decker.wheels.pl.
6. Verify the decker is straight (see the section on aligning a long slit); use tweak.decker.pl if necessary.
7. Measure the star centroids and write them to a stars file for xbox:
imexam logf=stars keep+
Type a on each star
8. Insert mosplate using config.mos.wheel.pl
9. Check the plate is straight on the array with by stretching the display to see the plate frames. If necessary,
use tweak.mos.pl.
10.Measure the box centers and write them to a box file for xbox: Measure the boxes in the same order as
you measured the stars.
imexam logf=box1 keep+
type e to generate a contour map
type g to get the graphics cursor
center the cursor on the box and type x
type i to return the image, and repeat this process for the other boxes.
If you cannot see the box well in the contour plot, consider starting over after setting the upper contour
limit threshold to ~5,000 ADU (epar eimexam).
10. epar xbox, and run it on the mask image; set the box and star file parameters to your imexam filenames,
then type go.
11.Type q to step through each of the boxes in the graphics window. If the box center is not clearly detected,
use the f key to force the center, and g to force the signal threshold.
12.After the last box it will tell you how much to rotate the mos wheel and offset the telescope.
Use guided.relative.offset.mmt.pl to offset in instrument coordinates.
Have the telescope operator increment the instrument position angle by the suggested rotational
motion; do not tweak the mos unless xbox is using the mos wheel's center of rotation for calculations.
13. Take another image. At this point you should have stars in boxes.
14.If you have rotated the mos wheel with respect to the detector, remeasure the boxes with imexam and
make a new box file.
15.Run xbox on the latest image, with no star file. After several iterations of offsetting and rotating the
telescope and taking images the mos plate should be aligned.
Note: if the alignment stars are faint, you may need to run xbox on images with some of the sky flux
subtracted. To do this take an image with no starts in boxes; scale this image by 0.8 (use imarith) and then
subtract the scaled image from the newest image; run xbox on the difference image.
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