Synphot Data User's Guide


2.5 Temperature specification (NICMOS, WFC3)

With the release of STSDAS 3.0, support for thermal calculations was added to synphot with the new task thermback. At present, this capability has only been fully implemented for NICMOS. For WFC3, thermback calculates the thermal background, but only does so at the default temperatures within the instrument (parameterized keywords do not yet apply to WFC3).

2.5.1 NICMOS

Additional keywords, including opaque but thermally emitting components of the OTA, were added, and all keywords except the detector keywords became parameterizable for temperature. Thus, to compute the thermal background assuming the primary mirror temperature is 290K, one would specify an obsmode nicmos,3,f222m,primary#290.0.

If no temperature value is specified, the default temperature for each component is used. The default temperature is stored as a header keyword (DEFT) in the thermal file for each component, which also contains the emissivity tables as a function of wavelength.

Most of the NICMOS optical elements are contained in the dewar, and are therefore at the same temperature. The software does not enforce this however: the user must specify the new temperature for each component individually. The keywords for the NICMOS components located in the dewar are reimag pupil image para1 para2 bend dewar cmask.

2.5.2 WFC3

No parameterized keywords are yet supported for WFC3. The default temperature is always used.

Note that for observation modes using a grism, the bkg keyword should always be specified with thermback, as discussed in Section 2.7.

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