A few notes
Morning / afternoon calibrations:
Flats in different IR filters require time, in particular with narrow
band filters. Please organize everything
in advance with the SA and OA, especially if you need flats on the
sky. In normal circumstances the dome has to be accessible to the daycrew
from 08:00am to 05:00pm, monday to friday, so please be aware that
telescope operations may conflict with your requests. The SA will also
let you know what calibration data are already available from previous
Staring or not?:
CFHT-IR can be used without closing its warm shutter, in what is called
its "staring mode", selected by "staring 1" in the detector window (or
in an observing script). The exposure time of staring mode exposures
is always a multiple of the readout time (enforced by the acquisition
program), and must be at least twice the readout time. The staring mode
has reduced overheads (no shutter cocking), and eliminates the
thermal background from looking at the warm shutter during readout (~800ADUs
for K, ~500 ADUs for K'). It also has more accurate timing than the
mechanical shutter. It is the recommanded observing mode, unless you need
exposure times below one second.
Make sure you use the blank filter position when obtaining darks.
The cfhtir shutter is WARM, and a very significant source of thermal
radiation (500 ADU/s with the K' filter, 800 ADU/s with the K filter,
for typical dome temperatures of a few degrees Celsius).
K band exposures on the shutter saturate in about 1~mn...
The detector exhibits a memory of having been saturated, that will affect
the next few subsequent exposures. This can for instance happen when obtaining
flat-field exposures with too long integration times, or while observing bright
sources. A cube of 8 0.1 second exposures second is usually sufficient to
clean the detector (unless you saturated it really badly, and many times).
Script detclean will do that for you
Copyright © 2003, CFHT Corporation. All
Changing the acquisition directory from the default (/data/piko/cfhtir)
is NOT recommanded: it adds an extra 4s to the readout overhead to access a
non-local disk. Files are automatically copied to ~cfhtir/images after a few
You are NOT allowed to change the filename ######x.fits (constraint
due to archiving). An odometer will automatically incremement this number.
After an integration, the name that appears in the DetI form is the
filename for the next exposure, NOT the one that just finished.