STScI Logo

Hubble Space Telescope
GRISMs

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:
Grism A (G096): F110W
Grism B (G141): F150W
Grism C (G206): F175W