FOS Instrument Science Report # 122

"FOS Pre-COSTAR Blue Side: Target Acquisition Accuracy"
by E. Vassiliadis, R. Bohlin, A. Koratkar, and I. Evans

Abstract excerpted from the report:
	Pointing accuracy of the FOS is examined after a sample of 12 
	planetary nebulae in the Magellanic Clouds are acquired using on-
	board binary search or peak-up acquistion modes.  Accuaracies are 
	determined from FOS images of the 4".3 aperture after completion of the
	normal acquisition modes.  The accuracies are measured with respect
	to the image center.  The location of the aperture center is unknown
	and does not necessarily coincide with the image center.  From 10 cases,
	the binary search acquistion mode is repeatable to 1_=0".08, but with
	a mean systematic offset from the image center of 0".09.  The
	uncertainity in the mean is 0".03.  The offset is predominantly in the
	X-dimension, and is also present in data presented by Caganoff, 
	Tsvetanov, and Armus in CAL/FOS-081.  The maximum uncertainity in the
	peak-up acquisition mode is 0".03 in each axis for the aperture and
	search pattern used here, and the results from the two objects 
	acquired with a peak-up indicate no systematic effect greater than	
	this uncertainity.




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