IRAC Instrument Handbook - IRSA - California Institute of Technology

IRAC Instrument Handbook
Example images of scattered light are shown here to alert you in case you see something similar in your
IRAC images. The scattered light pattern from point sources is difficult to predict, and very difficult to
model for removal. To the first order, you should not use data in which scattered light from point sources
is expected to cover or appears to cover your scientific target. Stray light masking is done in the pipeline.
This procedure incorporates our best understanding of the stray light producing regions. The procedure
updates the corresponding imask for a BCD by determining whether a sufficiently bright star is in a stray
light-producing region. The 2MASS point source list is used to determine the bright star positions.
Figure 7.12: Channel 2 image showing scattered light on one side of a bright star. The scattered light patches
are marked with white “S" letters. The images were taken from program PID 30 data.
Figure 7.11 to Figure 7.14 are 201 pixels (4.1’) square, and have been extracted from larger mosaics
produced from the IRAC GTO shallow survey (from program ID 30). This survey covers 9 square
degrees with three 30-second images at each position. Because the mosaics cover large areas, the star
causing the scattered light appears in many of the images. All of the sample images have the same array
orientation as the BCD images. The sample images are mosaics of a BCD that contains the stray light and
Data Features and Artifacts 122 Optical Artifacts