Background
The primary operational wavelength regime for DEIMOS is redward
of 5000 Å, and most of our DEIMOS observing
procedures are written under the assumption that red
calibrations are appropriate. DEIMOS can also be used in the
blue, but calibrations must be acquired in a different manner in
order to obtain optimal wavelength solutions and flatfielding
with the DEEP2 DEIMOS data reduction
pipeline. This document describes the procedure developed
by Evan Kirby of Caltech to achieve satisfactory blue
calibrations.
Procedure
A new DEIMOS script called calib_blue has been developed
for obtaining arc line and internal flat lamp calibrations which
are appropriate for use of DEIMOS in the blue. This procedure
is optimized for use with the 900ZD grating at a central
wavelength of 5500 Å. It takes separate arc and flat
exposures for the red chips and the blue chips. The red-chip
arc and flat images are not appropriate for the blue side and
vice versa.
Arc Lamp Exposures
For arc lamp exposures, the red chips use the standard
combination of lamps used in the main calibration script. The
arc exposure for the blue chips use a combination of lamps
optimized to get the most lines in the blue. Some lamps are
turned off during the exposure so that they do not saturate.
The active lamps will not be recorded properly in the FITS
header. The user must modify the FITS header to reflect all
five lamps that were on at some point in the exposure: Hg Cd Zn
Ar Kr. If the spec2d pipeline is
used for data reduction, separate arc exposures may be specified
in the plan file using the BLUEARCNAME and REDARCNAME keywords.
Flat Field Exposures
For flat field exposures, the script acquires three images for
the red side. Because the DEIMOS throughput is very low near
4000 Å, the script acquires six images for the blue
side. These exposures will saturate the red side. As written,
the spec2d pipeline will not accept separate red and blue flat
field images. However, it is reasonably easy to modify the
read_planfile.pro and
deimos_mask_calibrate.pro files to accept different
images. Interested users are welcome to contact Evan Kirby for
examples.
Time Requirements
The script requires about 23 minutes per mask to acquire the
calibration exposures. If one is short on time, then the user
may wish to modify the script to reeduce the time to warm up the
arc lamps.