Synphot Data User's Guide
2.2 Contamination (WFPC1, WFPC2)
cont#keyword references the Modified Julian Date, which is used to account for the gradual decline in throughput between decontamination events, as well as for the sudden increase in throughput immediately after a decontamination.
For WFPC1, data exists for 48384.0 < MJD < 49329.0 (8 May 1991 to 8 December 1993), in intervals of 20-30 days.
For WFPC2, data currently exists from MJD 49347.0 onwards (26 December 1993), in intervals of approximately 30 days.
The synphot expression evaluator interpolates between the dates for which data exists in the table to arrive at an estimate of the throughput on the requested date.
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