A model-based approach to the spatial and spectral calibration of NIRSpec onboard JWST

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Volume 592 (August 2016)

A&A, 592 (2016) A113

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Table 2

Summary of the parameters employed in the NIRSpec parametric model of the spectrograph.

			Number of parameters
Element	Type	Description	Total	Free


Optical module	Paraxial transform	Input plane center	2
COL, CAM		Output plane center	2
		Rotation angle	1
		Scaling factors	2
	Geometrical distortion	Forward 2D polynomials	21 × 2	21 × 2
		Backward 2D polynomials	21 × 2	21 × 2


MSA	Quadrant positions	Position of shutter (1, 1)	2 × 4	2 × 4
		Rotation angle	4	4
	Shutters	Pitch size	2 × 4	2 × 4
		Aperture size	2 × 4
	Fixed slits	Absolute position	2 × 5	2 × 5
		Aperture size	2 × 5


GWA	Dispersers	Alignment angles	3 × 8	3 × 6 ^†
	Grating dispersion	Front surface tilt	6
		Groove density	6
	PRISM dispersion	Front surface tilt	1
		Internal prism angle	1
		Sellmeier refractive index	8
		Temperature and
		pressure dependence	6


FPA	Detector positions	Position of pixel (1, 1)	2 × 2	2^‡
		Rotation angle	2	1^‡
	Pixel positions	Pitch size	2 × 2


IFU	Slicer position	Absolute position	2
		Rotation angle	1
	Slices	Relative position	2 × 30
		Aperture size	2 × 30
IFU-FORE	Optical module	Paraxial + 2D polynomials	7 + 21 × 2
IFU-POST	30 Opt. modules	Paraxial + 2D polynomials	(7 + 21 × 2) × 30	3 × 30 ^♣

Notes. All of the parameters needed to transform a point from one focal or pupil plane are listed here. The two last columns give the total number of available and free parameters in the optimization process described in Sect. 5.

^(†)

The prism was not included in this work and the mirror alignment was set to fixed angles.

^(‡)

Only for SCA492.

^(♣)

Only the center position and rotation of the output plane of each IFU-POST paraxial part were optimized.

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