IRAC Instrument Handbook - IRSA - California Institute of Technology

7.3 Optical Artifacts
7.3.1 Stray Light from Array Covers
IRAC Instrument Handbook
Stray or scattered light on the arrays can be produced by illuminating regions off the edges of the arrays.
Stray light from outside the IRAC fields of view is scattered into the active region of the IRAC detectors
in all four channels. The problem is significantly worse in channels 1 and 2 than in channels 3 and 4.
Stray light has two implications for observers. First, patches of stray light can show up as spurious
sources in the images. Second, background light, when scattered into the arrays, is manifest as additions
to the flatfields when they are derived from observations of the sky. The scattered light is an additive, not
a multiplicative term, so this will result in incorrect photometry when the flatfield is divided into the data
unless the scattered light is removed from the flat. Stars which fall into those regions which scatter light
into the detectors produce distinctive patterns of scattered light on the array. We have identified scattered
light avoidance zones in each channel where observers should avoid placing bright stars if their
observations are sensitive to scattered light.
Figure 7.10: An image of the M51 system, showing an overlay of the IRAC fields of view, with the scattered
light origin zones for channels 1 and 2 overlaid.
Data Features and Artifacts 120 Optical Artifacts