IRAC Instrument Handbook - IRSA - California Institute of Technology

Point Source Fitting IRAC Images
with a PRF
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IRAC Instrument Handbook
Figure C.1: PRF fits vs. aperture photometry for selected IRAC calibration star CBCDs. The
vertical axis is the fractional difference between the PRF fit and corrected aperture photometry.
The aperture photometry for IRAC channels 3 and 4 is in a 3 pixel radius with a 12–20 pixel
background annulus and an aperture correction factor from this Handbook. For IRAC channels 1
and 2, it is in a 10 pixel radius with the same annulus. Short black dashed lines are the expected
annulus correction nee ded. Long blue dashe d line is the offse t estimate d from a we ighted ave rage of
the data. Note this is essentially the expected value for IRAC channels 3 and 4. But IRAC channel 1
(and IRAC channel 2 to a lesser extent) requires a pixel-phase correction (see text).