Preliminaries

If you take dome flats in the morning after your observing night, be sure to use the commands endnight to put NIRC2 into safe mode and aohatch close to protect the adaptive optics bench when you are finished.

You can obtain at least broad-band flat fields by using the dome flat lamps designed for the optical instruments. Ask the OA to point to a good flat field spot on the dome (usually at an elevation of 45°) and turn on the spectral lamps. These are the bright lamps. Below is a table of exposure time estimates that should produce 8000 DN or somewhat less in each broadband filter and camera combination. Numbers in parentheses indicate that the exposure time is to short to reach with the full frame. Either a subarray can be used, or you can try using a flat field from the narrow camera to calibrate data taken with the wide or medium camera. Note that this technique has NOT been tested; it is only a suggestion.

Note also that there are two flat field lamps. If you see only 1/2 of the expected flux, there may be a burned out lamp. Ask the OA to check by looking for uneven illumination on the dome.

Procedure

The procedure for dome flats is:
  1. In any waikoko xterm type configAOforFlats and answer Y to the prompt (if you have checked beforehand with your support astronomer).
  2. Bring up the dome lamp control GUI found under Telescope GUIs → Dome lamp control on the VNC pulldown menu.
  3. Turn ON the Spectral lamps and confirm that you see flux on the AO WFS (and that OFF results in very little flux on the AO WFS). If this check does not work out, check the light path (e.g., AFM in SC gui, tertiary mirror position, etc)
  4. Alternatively you can use the DCS keywords for lamp control on a waikoko or vm-nirc2 terminal. The keyword that controls the imaging dome flat lamps is flimagin. The keyword that controls the spectal dome flat lamps is flspectr. The spectral lamps are brighter than the imaging lamps. Given the small pixel scale of NIRC2, we use the spectral lamps to take imaging flats. These are some examples of utilization of the DCS keywords to turn on and off dome flat lamps:
  5. Manually take the flats using the recommended times in the table below, or run a script (e.g., /home/nirc2eng/vis/arc/flat_examples/makeFlats)
  6. Make sure to Turn OFF the dome flat lamps once you are done taking your flatfield frames.
  7. If it is morning, follow the caution at the top of this page (endnight and aohatch close).

Exposure times

Filter
Camera
Notes
wide
narrow
z
12
120
 
Y
8
110
 
J
1.2
20
H
1.2
20
K
6
110
Kp
3
45
Ks
4.5
65
Lp
--
0.2
Pa gamma
30
360
 
Jcont
10
160
Pa Beta
10
160
Hcont
10
80
CH4_long
5
80
Fe II
15
240
CH4_short + PK50_1.5
-
30
He I A
35
360
 
He I B
25
400
Br gamma
90
160
H_2 1-0
100
1600
H_2 2-1
300
4800
Kcont
450
2700
CO
300
4800
Br gamma2
90
1600
H2O
1
16
PAH
1
16

Estimated exposure times in seconds for NIRC-2 dome flats.