Throughout this document, we assume that a resolution element (resel) spans 6 × 10 pixels on the FUV detector (in the dispersion and cross-dispersion directions, respectively) and 3
× 3 pixels on the NUV detector (
Table 1.2). These values were determined before launch. Even then, it was known that the true size of a resel would vary with wavelength. In-flight data suggests that the FUV resel is somewhat larger than previously assumed (see the discussion of the line-spread function in
Section 3.3), while the NUV resel is smaller. We will continue to refine our analysis of the instrument parameters. In the mean time, keep in mind that the
COS Exposure Time Calculator (ETC) uses the pre-flight resel sizes in all of its calculations. Users who adopt a larger or smaller resel should adjust the
ETC results accordingly.
