THE IMPLICATIONS OF ATMOSPHERIC EFFECTS FOR FIBER-FED SPECTROSCOPY

The effects of atmospheric dispersion in terms of S/N losses are calculated as a function of displacement of an optical fiber with respect to the source image. The results are presented as response curves for a wide variety of seeing conditions and source-to-sky brightness ratios. The limitations of fiber systems for precision spectrophotometry and ways in which these limitations may be overcome are discussed. The effects of differential refraction and field rotation are also calculated, showing that it can be a nonnegligible effect at large zenith angles for observations of more than 1-hour duration.