Synphot Data User's Guide


3.2 Specifying STIS observation modes

In the STIS instrument, imaging mirrors and gratings are contained in the mode select mechanism (MSM) while filters and slits are in the aperture wheel. Each grating or imaging mirror is intended for use with only one of the three STIS detectors (CCD, NUVMAMA, or FUVMAMA).

In principle, any filter or slit (aperture) could be used with any grating or mirror, although in practice certain combinations are restricted or forbidden.

Since the slits and filters are in the same wheel, it is not possible to use both a slit and a filter at the same time. (Some small slits contain built in neutral density filters.)

The ADC gain keywords only apply to the STIS CCD modes and are used to convert results from units of electrons to DNs.

In a synphot observation mode string, specifying the grating automatically determines the detector used.

Each central wavelength is intended for use with a particular grating. See the STIS Instrument Handbook for a listing of which central wavelengths are allowed with each grating. The low order gratings, G140L, G230L, G230LB, G430L, and G750L have only one allowed setting and a central wavelength should not be specified in the observation mode string.

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