Hokupa'a Observing Overheads

Each new science target may incur the following overheads:

• Configuration overhead of 30 minutes (e.g. to acquire the peripheral wavefront sensor and AO guide stars and optimise the AO control loop)
• Offseting to and from sky frames requires about 30 seconds. This includes the time to reacquire the star in Hokupaa.
• 20 minutes for each PSF calibration (e.g. if observing a separate PSF star is required).
• 20 minutes for photometric standard
• Once on target, a typical observation will consist of slighty offset (dithered) positions. Each offset currently requires opening servo loops, moving AO and PWFS sensors to the new guide star positions and closing loops. This process takes about 30sec and we are seeking to automate some aspects to improve efficiency.
• The QUIRC camera has an overhead of 15sec per frame (which can be in parallel with the offset overhead).

Overheads are estimated based on commissioning results as well as early QuickStart observations.

Example: As an example, 30 min of on-source integration comprised of three sets of 3*50sec exposures at each of four dither positions, separate sky frames using the same dither sequence and interspered with the science observation after each complete four position cycle, plus observation of a PSF star for photometry and deconvolution, would take about ~140 minutes.

30 minutes	(Target acquisition)
20	(PSF calibration)
12*0.5	(on-source offseting/dithering)
24*0.25	(on-source detector readout)
30	(on-source time)
12*0.5	(on-sky dithering)
24*0.25	(on-sky detector readout)
30	(on-sky time)
6*0.5	(switching between source and sky)
______________	_____________________________
137 minutes	TOTAL

If the target is extended or lies in a very crowded field then separate sky exposures would be required.

Last update 24 August 2000; Mark Chun