== P3.21	Star center == 
•	**Phase**		:	3  
•	**Status**		: 	Draft	 
•	**Category**		: 	Nighttime calibration (C5)
•	**Recurrence**	: 	on every target, starting from commissioning.
•	**Duration**		: 	20 minutes
**Description**
•	This calibration is performed to calibrate the target star center with respect to the detector in order to provide a reference input for frame derotation and quadrant combination. 
**Prerequisites**
•	Authorize SHARK-NIR on the SX side.
•	Atmospheric conditions: AO working conditions.
•	Bad pixel map, Dark 
**Procedure**
•	DM produce a pattern offset with four spots symmetric with respect to the star + AO closed-loop + coronagraph
•	The required specifications of the corresponding image are a grid of at least 2x2 regularly spaced focal plane image peaks within 5 and 15 lambda/D with FWHM < 45 mas and separation precision < 6 mas.
•	DM offset applied on target acquisition to produce a waffle image. Find the center of the four first-order diffraction peaks (cross geometry) to deduce the pixel corresponding to the center field.
**Success criteria**
•	Accuracy of 3 mas (goal 1 mas) 
**Notes**
•	Same as activity 7.8 in AD4
**LBTO support**
•	Support from LBTI/LBTO?
**Associated SHARK-NIR personnel**
•	JF, LM, MdP
**Date performed and by whom**