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Overheads at the NOT

Below you find tables with typical times for the different operations when observing at the telescope.

The execution time for a set of exposures as defined in an observing script is given as output from the script generator. The read-out time of the detector is included in the execution time, but is less for a windowed CCD (see instrument web pages ALFOSC, FIES, MOSCA, StanCam). Sum up the execution time of the observing script with the times needed for other operations (e.g., acquire the target, focus the telescope) to estimate the total execution time for a specific observation.

Telescope overheads
Target acquisition (imaging)3min
Target acquisition (spectroscopy)5min
Small step dithering (no autoguiding)6s
Small step dithering (autoguiding)15s
Large step dithering (beam switching, no autoguiding)20s
Mirror covers open (baffle lamp)1min
Mirror covers close (baffle lamp)1min
FASU overheads
Changing filter20s
Mirror motion (calibration lamps) 13s
ALFOSC overheads
Changing slit/filter/grism25s
Focusing telescope5min
Flat fields (typical time for 3 images in one filter)8min
Readout times (see this table for different windows)
ALFOSC Polarimetry overheads
Rotating the retarder (FAPOL)2s
Readout time polarimetry imaging (standard window)~ 6s
Readout time spectropolarimetry (default, vertical spectrum)~ 10s
NOTCam overheads
Target acquisition imaging 3 min
Target acquisition spectroscopy 5 min
Focusing telescope 5 min
Differential twilight flats (2 x 8 images), per filter/camera setup 8 min
Readout array (controller) 3.6 s
Clear array command 3.5 s
Data file storage time (for 4 to 32 MB files) 2 - 7 s
Readout overhead for "exp,mexp,dark,mdark" (per exposure) 8-9 s
Readout overhead for "frame t N" (t < 5s) 5-7 s
Readout overhead for "frame t N" (t > 5s) 4-5 s
Telescope dither 10" (ag-off) 3-9 s
Telescope dither 10" (ag-on) 7-9 s
Telescope dither 240" (ag-on) 8-20 s
Lens wheel WFC -> HRC 30 s
Lens wheel HRC -> WFC 50 s
Filter, stop, aperture & grism wheels30 s
Internal focus change25 s
notcam.easy-calib (1-5 wavelength regions)
1 argon, 1 xenon and 3 halogen per region
2 min per region
+ 1.5 min
Wavelength calibration (H and K-band WFC)3.5 min
See the NOTCam User's Guide for explanations of overheads
StanCam overheads
Focusing telescope5min
Flat fields 5min
Filter change30s
CCD probe25s
FIES overheads
Focusing telescope10min
Target acquisition2-5min
CCD probe20s
Fiber mask: typical20s
Fiber mask: worst case = between fibers #1 and #2 85s
Fiber calibration arm: typical12s
Fiber calibration arm: worst case = from fiber #4 to #165s
ThAr calibration exposure, all overheads included2m
FIES & StanCam overheads
CCD probe20s

Typical ALFOSC spectroscopy calibration exposure times in seconds (s).

Note that we have used 120 seconds as an upper limit for faint arc line and flatfield spectra.
For the flatfield lamps the exposure times aim for about 60000 ADU, and the expo times scale reversly with slit width (the values below are for a 1 arcsec slit).

lamp \ grism #3 #4#5#6 #7 #8#9+CD#10 #11 #12 #13+filter#14#16#17
He 3 3 3 10 3 3 10 8 3 3 20 3 20 --
Ne -- 3 3 -- 3 3 10 6 3 ? -- -- -- 2
ThAr 120453012012030120 60 -- 30 120 120120120
Halogen (internal) 40 1010 50 2530120 10 10 2 120 50120120
Blue (baffle lamp) 2 ---- 3 ---- ? -- -- -- ? 3 15 14

Typical NOTCam spectroscopy calibration exposure times in seconds (s).

The Halogen exposure times aim for a peak illumination of 25000ADU.

WFC + grism #1 + '128' slit
lamp \ filterZ Y YnJHK
Halogen 15 15 15 87 7
Argon 0.6 2 ? 1.52 10
Xenon 0.6 0.6 ? 15 1020

Note that the Argon lamp needs some starting up time (at least 10 seconds).

HRC + grism #1 + '44' slit
lamp \ filterJHK

Note that the Argon lamp needs some starting up time (at least 10 seconds).

Typical FIES calibration exposure times in seconds (s).

Exposure times for the Halogen lamps aim for 35K peak counts.
Exposure times for the ThAr lamps aim for 15K peak counts in the blue.
All values are for an unbinned CCD.

Please note that the exposure times needed for the FIES calibrations are fluctuating notoriously, and need to be checked at the start of the run.

Fiber bundle B (spare)
lamp\fiber fib#1 low-resfib#3 med-resfib#4 high-resfib#5 high-res calib
Halogen 10 0.7 1.5 3
ThoriumArgon6 2 16 1.5

Fiber bundle C (default)
lamp\fiber fib#1 low-resfib#2 med-resfib#3 med-resfib#4 high-resfib#5 high-res calib
Halogen 0.8 1.5 0.8 1 11
ThoriumArgon2 2 2 4 5

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