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A new geometric distortion solution for the STIS NUV MAMA

A new geometric distortion solution for the STIS NUV MAMA. Jes ús Maíz-Apellániz Leonardo Úbeda TIPS 17 July 2003. Why?. Original motivation: NUV-MAMA objective-prism utility Current implementation based on Walsh et al. 2001 gives large errors

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A new geometric distortion solution for the STIS NUV MAMA

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  1. A new geometric distortion solution for the STIS NUV MAMA Jesús Maíz-Apellániz Leonardo Úbeda TIPS 17 July 2003

  2. Why? • Original motivation: NUV-MAMA objective-prism utility • Current implementation based on Walsh et al. 2001 gives large errors • New approach: use well-known PC geometric distortion to obtain solution for NUV MAMA

  3. Data • Central region of NGC 4214 • WFPC2 • GO 6716, P.I.: Stecher F170W F336W angle 1: u4190101r, 02r u4190103r , 04r angle 2: u4190201m, 02m u4190203m , 04m • NUV MAMA • GO 9096, P.I.: Maíz-Apellániz CN182 CN270 angle 1: o6bz02isq, iwq o6bz02j7q , jbq angle 2: o6bz01afq,(akq) (o6bz01b1q),(b3q)

  4. Positions of the PC fields

  5. Positions of the NUV-MAMA fields N E MAMA angle 1 PC angle 2 MAMA angle 2 PC angle 1 F336W PC mosaic

  6. Technique • Find stars and measure positions (and photometry) with HSTphot in PC data • Measure rotation and displacement between PC fields and merge lists • Measure rotation and displacement between PC and MAMA fields • Find stars in MAMA fields using merged PC list and centroid positions • Calculate and test geometric distortion

  7. Geometric distortion model • Direct (pixel  sky ) • xc = i=0,kj=0,iai,j·(x-xr)j·(y-yr)i-j • yc = i=0,kj=0,ibi,j·(x-xr)j·(y-yr)i-j • Inverse (sky  pixel) • x = xr + i=0,kj=0,ici,j·xcj·yci-j • y = yr + i=0,kj=0,idi,j·xcj·yci-j • xr = yr = 512 • k = 3,4,5

  8. Testing • Consistency check of the PC solution • F336W vs. F170W PC data • Polynomial degree • Weighting schemes • Distance between 2 PC positions • Magnitude cut • Single-field vs. multi-field solutions • CN182 vs. CN270 differences • Comparison with Walsh et al. 2001 (ISR) • External testing

  9. Consistency check of the PC solution

  10. F336W vs. F170W data N o: F170W + F336W o: F336W E

  11. Polynomial degree

  12. Testing • Consistency check of the PC solution • F336W vs. F170W PC data • Polynomial degree • Weighting schemes • Distance between 2 PC positions • Magnitude cut • Single-field vs. multi-field solutions • CN182 vs. CN270 differences • Comparison with Walsh et al. 2001 (ISR) • External testing

  13. CN182 vs. CN270 differences

  14. Detector coverage

  15. Comparison with Walsh et al. 2001 Walsh et al. 2001

  16. Comparison with Walsh et al. 2001 uncorrected

  17. Comparison with Walsh et al. 2001 original correction

  18. Comparison with Walsh et al. 2001 corrected

  19. Comparison with Walsh et al. 2001 uncorrected original correction corrected

  20. Plate scales

  21. External testing

  22. Added bonus: testing PC photometry

  23. Summary • New geometric distortion solution for NUV MAMA • Provides positions with median uncertainties of 0.4 MAMA pixels (10 mas) • No wavelength dependence detected in plate scale or distortion but testing not quite complete • PC astrometry and photometry in the UV is quite precise after all corrections are applied

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