Synphot Data User's Guide


2.3 Modified Julian Date (ACS, STIS)

The mjd keyword is used to handle the time dependent sensitivity of certain instrument detectors. It may be applied to all ACS modes; for STIS, it applies only to the MAMA grating and imaging modes (it has not yet been implemented in synphot for the MAMA echelle modes) and sensitivity of the FUV and NUV MAMAs. To use this capability in simulations, include the string mjd#ddddd in your obsmode specification, where ddddd is the desired MJD value (which can be given as either an integer or real value).

For example, to get the efficiency on MJD 49486, use "mjd#49486" as part of your obsmode string. When specifying the mjd keyword in command line input to synphot, it may be necessary to enclose the obsmode string in quotes to ensure that the synphot expression evaluator properly interprets the obsmode string.

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. The default is to use the latest set of throughput values without any extrapolation. The values are expected to be updated approximately yearly, so the default result should not differ by more than 2 percent from those that use the current date.

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