Q.: How many rolls are needed to deconvolve extended or multiple
targets in the GRISM?
A.: Observations of extended or multiple objects with the GRISMs can
result in overlapping spectra that must be separated during data
analysis. By observing a particular field at multiple roll-angles
it is possible to remove the degeneracy present in a single
observaton. There is no single rule that can be quoted for all
possible targets. General advice would be to obtain spectra at
three or four spacecraft orients over a range as large as possible
up to 90 degrees. Grism observers are also reminded that it is
essential to obtain a matching filtered image for each grism
observation so that sources can be located in the field of view.
Q.: For spectroscopy, when do I need to pair the Grism observation
with a broad-band filter observation?
A.: Whenever the number of objects within the Field of View of Camera 3
is large enough to potentially create problems in the identification of
individual spectra, a broad-band image should be obtained in Camera 3.
Suggested paired filters are: