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WFC3 SMOV UVIS and IR Geometric Distortion Calibration and Multidrizzle

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

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WFC3 SMOV UVIS and IR Geometric Distortion Calibration and Multidrizzle

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  1. WFC3 SMOV UVIS and IR Geometric Distortion Calibration and Multidrizzle Vera Kozhurina-Platais and WFC3 team

  2. Astrometry is the base….

  3. Displacement of UVIS detector position due to distortion 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 The UVIS and IR channels have ~7% linear distortion, caused by inclination of the camera focal plane to the principal telescope axis

  4. WFC3 Geometric Distortion Goals of the SMOV Geometric Distortion Calibration: • Required Accuracy: UVIS - 0.2 pixels (8 mas) IR - 0.2 pixels (26 mas) • Deliver IDCTAB for Multidrizzle

  5. Standard Astrometric Catalogs and UVIS/IR observations • 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 • 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

  6. UVIS XY residuals wrt 47Tuc Standard Catalog IR H (F160W) magnitudes wrt 47Tuc Standard Catalog V magnitudes (F606W) IR XY residuals wrt 47Tuc Standard Catalog CMD of globular cluster 47Tuc 47Tuc stars SMC stars UVIS and IR Geometric Distortion Model • 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:

  7. XY residuals for WFC3/UVIS chip (LMC image) High-frequency, low amplitude XY residuals from the polynomial fit for UVIS chip. 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 Y (pix) X (pix) UVIS High - Frequency Distortion • XY residuals across WFC3/UVIS chip in vertical and horizontal slices

  8. From XY detector coordinates to IDCTAB Schematic illustration of the WFC3 UVIS (IR) detector coordinate system and V2V3 system = ORIENAT - PA_V3 Aj,Bj are an arrays of coefficients from the polynomials IDCTAB - Instrument Distortion Correction Table ( Hack & Cox, 2001 ACS-ISR-0108)

  9. 2-D XY residual map: drizzled IR frame of 47Tuc wrt Standard Astrometric Catalog Scaled by factor of 200 RMS of linear fit - 0.07 pix - 3 x times better of SMOV requirement Multidrizzle Results with newly derived IDCTAB • 2-D XY residual map: drizzled UVIS frame of 47Tuc wrt Standard Astrometric Catalog Scaled by factor of 2000 RMS of linear fit - 0.05 pix - 4 x times better of SMOV requirement

  10. ERO WFC3 Images

  11. 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 • New updated UVIS and IR IDCTABs will be released in January 2010 • 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.

  12. Residual Filter - Dependency Distortion

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