This checklist describes the "emergency" LRIS-style procedure
for aligning multiobject slitmasks on DEIMOS when the image
header is faulty and does not contain the typical information on
the positions of the alignment boxes.
Setup
The following steps would ideally be done in the afternoon in
order to save time on sky; however, they can also be done during
the night.
Acquire direct slitmask image. This can be done in
the afternoon via the DEIMOS Slitmask Imaging
Widget, or can be an alignment image acquired on-sky as
part of the fine alignment procedure.
Create box coordinates file.
In IRAF, use the check_boxes command to mark
locations of the alignment boxes. Launch the program
via:
check_boxes imagemaskname.box autogen-
where image is the name of the image to display
and maskname is the name of the slitmask.
When check_boxes displays the image,
center the cursor within an alignment box (use the arrow
keys for fine-tuning) and press the m key to
mark the box. Repeat for each box.
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
epar xbox to edit the parameters for the
xbox task. Set the input parameter
to the name of the box coordinates file you generated
earlier with check_boxes.
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.