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Knowledgebase: IRAC
How do I know if sources in my IRAC data are saturated?
Posted by Seppo Laine on 29 January 2009 02:18 PM

There are several things you can do to check for saturation. If you have HDR data, the saturation flag in the imask file of the long frames (bit 13) will be set. Similarly the same bit will be set in the imask if saturation is indicated during linearization correction. However, the best bet may be to look at the raw frames (*dce.fits frames). If any pixels near the core of your target approach 35,000–45,000 DN (30,000 DN in the warm mission; DN is the unit in the raw or DCE frames is DN), then the odds are that the central pixel itself is saturated (negative or positive values are seen in the channel 1 & 2 raw files so look for absolute values that approach 35,000).

If the data are clearly above saturation, a "donut" will be seen in the core of the source in the BCD image (the central pixel or pixels have smaller brightnesses than the surrounding pixels). This is a sure sign of saturation. Performing photometry on each BCD is useful too. If a source is just saturating, then it may not saturate in frames where the center of the star is at a pixel edge or corner.