B.3 IR Channel

The IR detector field of view is nominally concentric with the UVIS field, but subtends a somewhat smaller area on the sky, 136 × 123 arcsec. The detector tilt is about the x-axis (AXIS1 in Figure 7.1), so the projected aperture shape is nearly a rectangle, with the angle between the x- and y-axes on the sky nearly 90°, as shown by the outline in Figure B.3. At field center, the x- and y-scales are 0.135 and 0.121 arcsec/pixel, respectively. A vector plot of the deviation from linearity is given in Figure B.3. The deviations have been magnified by a factor of 10, as in Figure B.1. The largest deviation is 10 pixels, corresponding to about 1.4 arcsec.

Figure B.3: Linear components (crosses) and non-linear components (vectors, magnified by 10) of the geometric distortion on the WFC3/IR detector.

A map of the variation of pixel area across the IR detector to be used for correction of point-source photometry from images that have not been distortion-corrected (see http://www.stsci.edu/hst/instrumentation/wfc3/data-analysis/pixel-area-maps) is shown in Figure B.4. The ratio of maximum to minimum pixel area is 1.090.
Figure B.4: Variation of the effective pixel area with position on the IR detector. Darker shading indicates pixels with smaller area. Contours are drawn at 2% increments.