Synopsis: Different plates used for DASCH photometry used emulsions with different color sensitivities — equivalent to placing different filters in front of a CCD camera. Historically, the DASCH data did not make it easy to tell which measurements come from which emulsions, potentially leading to apparent "variability" that is actually a color effect.

Mitigation

DR7 data products now include “colorterm” data that can be used to infer each plate’s color response. See the Colorterms reference page for details.

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