Wavelength errors in spectrographs. I: the effect of surface irregularities in camera mirrors.
High-dispersion astronomical coudé spectrographs frequently give lower-precision radial velocities than expected. This is explained i part in terms of the variable spectral shifts along the plate produced by a camera mirror with zonal imperfections. For a mirror with a sinusoidal zonal irregularity, the standard deviation in the radial velocity depends inversely on the angular dispersion and size of the grating or prism and directly on the amplitude of the surface fluctuation. For a 300-mm grating with 1200 lines/mm used in first order at lambda = 0.5 microm, a standard deviation of 0.06 km/sec is obtained for a single measurement if the surface has a peak-to-valley fluctuation of 1/20 wavelength of green light.
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