Developments

This method of combination can be generalized to spectra with non-constant steps if the separation between the steps is known, or can be computed from cross-correlation. Thus, for ground-based spectra, strategies for obtaining data with small shifts in wavelength and position on the detector are common in assisting with reduction of pixel-to-pixel noise. To this data the Richardson-Lucy method could be applied to combine the seperate spectra and improve the spectral resolution. The resolution can thus be improved beyond that imposed by the diode width, provided that the achievable instrumental resolution is less than one diode, which is usually the case in modern spectrographs with current CCD's when the slit is narrowed. Thus the pixel size of the CCD need not be seen as a limiting factor in design of spectrographs. The absolute size of the CCD limits the simultaneous wavelength coverage, whilst pixel size can be effectively reduced by sub-stepping strategies and optimal combination of the data.

References

Ball Aerospace Group 1992, Final Report, GHRS Science Verification Program for the Hubble Space Telescope

Lucy, L. B. 1974, AJ, 79, 745

Lucy, L. B., &Baade, D. 1989, in 1st ESO/ST-ECF Data Analysis Workshop, P. J. Grosbøl, F. Murtagh, &R. H. Warmels, eds., European Southern Observatory, Garching, 219

Press, W. H., Flannery, B. P., Teukolsky, S. A., &Vetterling, W. T. 1987, Numerical Recipes - The Art of Scientific Computing, Cambridge University Press, Cambridge

Skilling, J., Strong, A. W., &Bennett, K. 1979, MNRAS, 187, 145