wfc3 smov uvis and ir geometric distortion calibration and multidrizzle
DESCRIPTION
WFC3 SMOV UVIS and IR Geometric Distortion Calibration and Multidrizzle. Vera Kozhurina-Platais and WFC3 team. Astrometry is the base…. Displacement of UVIS detector position due to distortion is ~140 pixels or 6 arcseconds. Displacement of IR detector position due to - PowerPoint PPT PresentationTRANSCRIPT
WFC3 SMOV UVIS and IRGeometric Distortion Calibration
and Multidrizzle
Vera Kozhurina-Plataisand
WFC3 team
The UVIS and IR channels have ~7% linear distortion, caused by inclination of the camera focal plane to the principal telescope axis
Displacement of UVIS detector position due todistortion is ~140 pixels or 6 arcseconds
Displacement of IR detector position due to distortion is ~35 pixels or 4 arcseconds
WFC3 Focal Plane & Geometric Distortion
Required Accuracy: UVIS - 0.2 pixels (8 mas) IR - 0.2 pixels (26 mas)
WFC3 Geometric Distortion
Deliver IDCTAB for Multidrizzle
Goals of the SMOV Geometric Distortion Calibration:
Observations: SMOV calibration programs (PI-L.Dressel):
UVIS 11444 : 47Tuc and LMC through F606W with dither POSTARGS
IR 11445 : 47Tuc and LMC through F160W with dither POSTARGS
Standard Astrometric Fields (Anderson, ACS-ISR-2006 & private communication)
47Tuc observations with ACS/WFC (F606W) mean epoch - 2004. 9 precision 1 mas
LMC observations with ACS/WFC (F606W) mean epoch - 2006. 4 precision 1 mas
Standard Astrometric Catalogs
and UVIS/IR observations
Geometric Distortion Model represented by 4th order polynomials:
U = A0 + A1X + A2Y + A3X2 + A4XY + A5Y2 + A6X3 + … + A14Y4
V = B0 + B1X + B2Y + B3X2 + B4XY + B5Y2 + B6X3 + … + B14Y4
where U,V are tangential-plane positions in the astrometric catalog X,Y are measured positions in UVIS chips or IR frames, normalized to the center of chip/frame Aj and Bj are obtained by Least Squares minimization
XY residuals wrt Standard Astrometric Catalogs:
UVIS XY residuals wrt 47Tuc Standard Catalog
47Tuc starsSMC stars
IR XY residuals wrt 47Tuc Standard Catalog
IR H (F160W) magnitudes wrt 47Tuc Standard Catalog V magnitudes (F606W)
CMD of globular cluster 47Tuc
UVIS and IR Geometric Distortion Model
XY residuals for WFC3/UVIS chip (LMC image)
UVIS High - Frequency Distortion
High-frequency, low amplitude XY residuals from the polynomial fit for UVIS chip.
XY residuals across WFC3/UVIS chip in vertical and horizontal slices
X (pix)
Y (pix)Structure of high - frequency distortion depends on location on the CCD chip.This is fine-structure in the F606W filter most likely due to manufacturing process
From XY detector coordinates to IDCTAB
Schematic illustration of the WFC3 UVIS (IR) detector coordinate system and V2V3 system
IDCTAB - Instrument Distortion Correction Table ( Hack & Cox, 2001 ACS-ISR-0108)
= ORIENAT - PA_V3
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CX j =−A j
B j
⎡
⎣ ⎢
⎤
⎦ ⎥×
cosθ
sinθ
⎡
⎣ ⎢
⎤
⎦ ⎥
CY j =A j
B j
⎡
⎣ ⎢
⎤
⎦ ⎥×
sinθ
cosθ
⎡
⎣ ⎢
⎤
⎦ ⎥
Aj,Bj are an arrays of coefficients from the polynomials
€
θ
Multidrizzle Results with newly derived IDCTAB
2-D XY residual map: drizzled UVIS frame of 47Tuc wrt Standard Astrometric Catalog
Scaled by factor of 200RMS of linear fit - 0.07 pix - 3 x times better of SMOV requirement
2-D XY residual map: drizzled IR frame of 47Tuc wrt Standard Astrometric Catalog
Scaled by factor of 2000RMS of linear fit - 0.05 pix - 4 x times better of SMOV requirement
Conclusions
Geometric Distortion derived from SMOV calibration is accurate to:
UVIS - 0.05 pixels (2 mas) 4x better than SMOV requirement
IR - 0.07 pixels (8 mas) 3x better than SMOV requirement
Geometric Distortion will be further improved in Cycle 17:
UVIS and IR multi-wavelength geometric distortion dependency
applying better centering technique using ePSF library
Detailed description of the Geometric Distortion calibration is in:
WFC3-ISR-2009-33 by Kozhurina-Platais, et.al.
WFC3-ISR-2009-34 by Kozhurina-Platais, et.al.
New updated UVIS and IR IDCTABs will be released in January 2010