Interesting object

https://www.legacysurvey.org//viewer-dev/?ra=187.5352&dec=-56.8625&layer=decaps2&zoom=16

This green line is an artifact known as a cosmic ray.

Interesting that it seems to be moving toward the mirror and goes from out of focus to in focus (seemingly)

The funny thing about cosmic rays is that they hit the CCD detector directly, rather than bouncing off of mirrors and getting diffracted by glass – they’re charged particles rather than photons, so they wouldn’t even bounce off a mirror :slight_smile: I’m not sure why this one seems to get broader to the upper-left though! Normally they come in and bounce off atoms in the detector, liberating electrons as they go (and those electrons get measured as signal in the image), leaving sometime long but usually thin streaks.
cheers,
dustin

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Maybe outlier rejection had a go at masking, but didnt do so well?

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I’m actually not certain whether the DECaPS2 processing used the same outlier-rejection code as the other layers. It seems to have more visible CRs, even in regions that should have multiple coverage.

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The plane is a complex astrometric background. Outliers are less obvious maybe.

DECaPS2 used the cosmic ray mask provided by NOIRLabs in the “Community Pipeline” but this is known to not work well in crowded fields and with structured backgrounds. Since spurious detections on cosmic rays are filtered at the detection-> object combination stage, we did not try harder to apply a better cosmic ray detector.

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