What is the FUSE dispersion and plate scale?
A. The SiC channels have a dispersive plate scale of 1.03 Angstrom/mm and the LiF channels have a scale of 1.12 Angstroms/mm. The dispersion direction for FUSE is also called the X-direction and each X-pixel covers 0.006 mm. Thus, the dispersions are 0.0062 Angstroms/pixel and 0.0067 Angstroms/pixel for the SiC and LiF channels, respectively. Each X-pixel subtends 0.545 arcsec and each Y-pixel (i.e., the direction perpendicular to dispersion) subtends 0.909-1.46 arcsec, depending on which grating/detector combination is used. (Notice that the FUSE pixels are not square.) Putting all of the above together, we get SiC side: 0.0114 Angstroms/arcsec LiF side: 0.0123 Angstroms/arcsec These formulas can be used to determine the widths of each of the FUSE slits in Angstroms. However, note that the resolution actually achieved for the narrowest (1.25″) slit will be somewhat degraded relative to what you calculate from the above relations due to optical aberrations in the spectrograph.
