Permanently mounted on the Nasmyth platform of Keck I, HIRES is extremely stable and not
impacted by flexure-induced distortions common to Cassegrain-focus instruments. Consequently,
calibrations are not typically required for each target unless extraordinary (m/s level)
velocity precisions are needed. It is therefore recommended that internal calibrations be obtained
at the beginning and/or end of the night. It has been reported that the cross-disperser and
echelle angles drift slowly (thousandths of a degree) throughout the night. Some observers
may want to obtain a set of calibrations near the half-way point to confirm the stability
of their instrument set-up and to better constrain the rate of change if detected.
A set of calibrations typically consists of several bias frames, internal flat fields
(labeled quartz1 and quartz2), and ThAr arcline exposures (ThAr1 or ThAr2).
Darks may
also be obtained, but given the low level of dark current present within the detectors,
are not necessary for most programs.
The calibration aquisition GUI which is launched upon starting the HIRES control
software, provides a straightforward and automated means of obtaining desired calibration
files.
To use the GUI, simply enter the desired number of bias frames, the number, exposure time,
desired calibration lamps, and filters for the flats and arcs, and the number and integration time
for any darks. After starting the sequence, a pop-up window opens summarizing the desired
calibration images. If everything is correct, proceed with the script. If corrections need
to be made, make them and restart the script.
Typical integration times for quartz lamp exposures are 2-5 seconds while ThAr lamp exposures
are 1-2 seconds. The ThAr2 lamp operates at 20 mA and provides brighter arclines in the blue.
The ThAr1 lamp is set to 8 mA and is generally used for red cross-disperser settings. Both
of these amperages can be modified, however, using the keywords CATCUR1 and CATCUR2 for
ThAr1 and ThAr2, respectively. The ng3 filter is generally used for both internal quartz lamp
exposures and arclines. Other filters, however, are available from the calibration acquisition
GUI or from XHIRES.
FLATFIELD for Blue orders:
- Exposure with typical exposure times to get sufficient counts in red orders (i.e. 2-5 sec depending on slit size, using quartz1 or 2)
- Exposure longer to get the needed counts in Blue, while the red orders saturate. We’ll need to calibrate this, I think its around 15-20 sec exp time.
