Synphot Data User's Guide

3.2 Specifying STIS observation modes

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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.

• If no aperture or filter is specified, the calculation is done for the clear aperture case. So the observation mode string "stis,g430l" is equivalent to either "stis,ccd,g430l" or "stis,ccd,g430l,50ccd", (50CCD being the unobstructed full field aperture for the CCD detector).
• If the detector name is specified without a grating, e.g., "stis,ccd,f28x50lp", it is assumed that an imaging mirror is being used.
• If no central wavelength is specified, e.g., "stis,ccd,g430m,52X0.2", results for the entire bandpass of the instrument will be calculated, while if a central wavelength is included, e.g., "stis,ccd,g430m,52X0.2,c4451", the calculation will be restricted to the actual wavelength range covered by that wavelength setting.

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.