Quick Review
- Focus the telescope using MIRA: recommended
- Coarse Alignment
- Select Appropriate Pointing Origin (Pickoff or LRIS)
- Put a guide star at the pickoff mirror guiding location
- Start Guiding.
- Fine Alignment
- Image the mask: stars are now in the alignment boxes
- Run check_boxes/do_lbox for fine alignment
- Repeat Fine Alignment if necessary.
- Start Spectroscopic Observations
Slitmask Alignment
This checklist describes the procedure for aligning
multi-object slitmasks on LRIS, assuming there are:
- alignment boxes in the multi-object slitmasks.
- pickoff mirrors will be used during coarse alignment.
- LRIS IRAF routines will be used for alignment.
Focusing the telescope before aligning a slitmask is recommended.
The focus is strongly dependent on the LRIS physical
rotator position and, to a lesser extent, the telescope elevation.
It is generally recommended to re-focus the telescope when the
telescope elevation angle has changed by 30° or more,
and/or the instrument's physical rotator position
(displayed as drive on the FACSUM display) has
changed by 45° or more. In practice, this often means
that refocusing is done for each slitmask, since each mask may
have a different rotator position.
- Tell the OA the name of your target as
listed in your star list file and also the position
angle for the instrument rotator.
- Ask to OA to run MIRA in the neighborhood
of your target.
- If you plan to observe the field for two
hours, you may ask the OA to run MIRA one hour ahead of
of your target field.
- MIRA on the blue side
should usually be run to focus the telescope because it
requires less time to re-configure the instrument.
- MIRA on the red side should
be run only if a good focus is critical to science
observations on the red side.
- Target name and coordinates
- Position angle (skypa)
- Pointing origin (should be LRIS)
In these steps, we put the stars into the alignment boxes using
the pickoff mirror by locating the guide star in the appropriate position
on the guider.
- Slew to the target
- Insert the slitmask that has a pickoff mirror.
- Tell the OA to switch to the slit-viewing guider.
- Slew to the target coordinates:
Inform the OA to either slew to the
- guide star coordinates with the Pointing Origin set to Pickoff.
- Coordinates of the mask center with the Pointing Origin set to LRIS.
After slewing, the alignment star should be visible on the pickoff mirror in the slit guider.
If it is not visible, try the following:
- Tell the OA to check pointing.
- Slew back to guide star and see if it lands on the pickoff mirror.
- If the above two steps fail, then proceed with the
slitmask alignment without pickoff mirror procedure.
- Center the star
Provide the OA with the guider coordinates to which the guide star should be centered.
- Please review Pickoff Mirrors to determine the correct location of the guide star on the guider.
- The location of the guide star is slitmask design software dependent.
- Begin guiding
Verify that the guide star location is correct by using the cursor on the
guider eavesdrop display.The alignment stars should now be in their boxes;
proceed with fine alignment.
In this step, we refine the positions of the stars within
their respective alignment boxes to achieve optimal
centering of the slitmask.
- Start Guiding:
Have the OA select a guide star on the movable
guider 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.
- Take an image.
- Start IRAF:
Select from the desktop menu:
IRAF and IDL --> IRAF --> cl + ds9
- load the keck package and the
lris sub-package
While in the IRAF xterm, load the keck package and the
lris sub-package. This should load the routines check_boxes, do_check_boxes
lbox, do_lbox, and other routines.
- cd to the data directory.
type cdata to change to the LRIS data directory. If this fails try the two steps below.
- If you do not know the data directory, type "s outdir" in a lrisserver window.
outdir = /sdata240/lris1/2000feb07 (unix path name)
- In the iraf terminal type:
cd /s/sdata240/lris1/2000feb07
The "/s" is required to access a summit directory from headquarters.
- Run do_check_boxesb or
do_lbox
- do_check_boxes
- waits for the image to complete writing to disk
- displays the image
- reads and overlays box positions on image
- allows observers to adjust and move box positions
- launches lbox
- do_lbox
- waits for the image to complete writing to disk
- launches lbox
- Repeat steps 2 and 6 if necessary.
Until the translation and rotation are within your tolerances,
repeat steps 2 and 6. Typically, a mask is aligned when the translation
and rotation are within the measurement errors given in parenthesis.
- The lbox and lbox routines will report suggested moves in
rotation and position, as well as the
uncertainties (in parenthesis).
- Perform another alignment iteration if:
- a rotator move was required
- either the north or east offset was >
0.2 arcsec (or whatever your personal
tolerance is!)
- Reconfigure the instrument for spectroscopy:
- Set dichroic and grism to the appropriate
position for spectroscopy
- Set blue filter to clear position
- Set blue camera focus as appropriate for the
clear position.
- Set exposure time as desired for spectroscopy.
- Expose...!