Overheads

Programs are typically run in queue. It is important to to be aware of overheads when receiving your allocated time. The time allocated to each program is clock time and includes acquisition, calibrations, and other detector and telescope overheads. 

Obtaining astronomical observations at any telescope will typically face four different sources of overhead: from the telescope, instrument, detector and any operation that requires human interaction. The Table below summarizes these overheads.

Source of Overhead	Action Type	Typical Time [sec]	Maximum Time [sec]
Telescope	Preset	75	300
	Pointing Correction	150	300
	AO setup	180	240
	Dither(AO)	3	20
Instrument	Camera, Pupil Alignment	60	300
	Filter Changes	10	60
	Troubleshooting	5	1800
Human Element	Field/Source Identification	5	300
	Imaging Alignment/Setup	20	300
	Ales Alignment/Setup	300	900
	NRM Alignment/Setup	300	900
	Nulling Alignment/Setup	600	3600
	Troubleshooting	60	1800
Source of Overhead	Action Type	LMIRCam [sec]	NOMIC [sec]
Detector	Fast Mode Full frame
	Medium Mode Full frame
	Slow Mode Full frame

Note that Fast mode has subwindowing.  Minimum time scales linearly with vertical pixel length.

The above times are estimates and may be refined.  Detector times TBD

Twilight is used for initial AO setup and checkout and for the initial instrument alignment. As a result, start of night set up overheads are therefore not passed on to the users. Calibration frames, such as Darks, are taken during telescope transition states while waiting for the AO to reacquire as another means of increasing observing efficiency. For ALES observations, it is necessary to take the wavelength calibrations before moving any optics to ensure consistent results. It may be necessary to take these during the night depending on the programs. These wavelength calibrations take approximately 20 minutes.