IRAC: Skyflats

Pixel-to-pixel gain variations are calibrated in IRAC by flatfielding using images of the diffuse zodiacal background. At least one region near the ecliptic plane is observed in every IRAC campaign.

These data are processed by a calibration pipeline similar in many respects to the BCD pipeline. Eventually, the data are stacked using a sophisticated outlier rejection scheme to remove the stars and galaxies from the data. The result is an image of the zodiacal background free of foreground and background objects. From this is subtracted a contemporaneous skydark, and the result normalized to one to create a skyflat.

After the first year of operations, analysis of the time history of the skyflats indicated no detectable change in the pixel-to-pixel response. The first year of skyflat data were combined into a set of "super skyflats." These skyflats have extremely high photometric S/N (~ 0.5, 0.3, 0.2, and 0.06% in channels 1-4, respectively), and are substantially free from residuals from stars and stray light. However, users are cautioned to read this page for important information regarding the accuracy of these flats for certain types of observations.

These flats are divided into all the BCD data by the BCD pipeline via the software module FLATAP. At this time (S13), all BCD images are processed with the same set of flats linked below.

FITS images of the IRAC skyflats.