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Spectral resolution

The instrument provides slit-limited resolution over the entire camera field and over the entire wavelength range. This means that the resolution is limited not by the point-spread-function of the spectrograph optics, but by the detector pixel size; the wavelength resolution is equal to the spectrograph dispersion multiplied by the spatial resolution of the detector.

For a CCD the spatial resolution of the detector is determined entirely by sampling considerations, and can be considered equal to two detector pixels. The situation is more complex for the IPCS, where the detector point spread function may be significant compared to the pixel size (see the IPCS-II User manual).

The detectors which might be used with UES currently include EEV and Tektronix CCDs, with pixel sizes of 22.5 m and 24 m respectively, and the IPCS-II providing a spatial resolution of 30 m. The resolving power for each of these detectors is summarised in Tab. 17, obtained by combining these numbers with the linear dispersion given in Tabs. 16 and 15). The resolution in km/s is also given. Both of these numbers are independent both of the wavelength, and the echelle being used. The resolution in Angstroms will of course vary with wavelength, and the table gives figures at a few representative wavelengths.

Mon Mar 14 16:50:31 GMT 1994