Line Photometry and the Influence of the Eberhard Effect

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Abstract
Spectrophotometric measurements on emission lines frequently involve the use of continuum standards, necessitating integration of the instrumental line-spread function. Such a procedure may lead to large errors due to such factors as the Eberhard effect, turbidity, and finite width of analyzing slits. An experimental method is described whereby the composite effect of all these factors can be assessed on a quantitative basis. The method was applied to two high-speed films (Kodak 4X negative and 2475 emulsions), machine developed to a high degree of uniformity. For low-density line images no significant sources of error were found and absolute intensities to an accuracy of ±5% were indicated, implying that a one-dimensional integration of scattered light within the emulsion correctly accounts for all of the light within the line. At higher density levels, measured intensities were found to be up to a factor of six too high because of the Eberhard effect. Reproducible correction factors generated by this method can be applied to line data taken with any arbitrary instrument (spectrum lines, point streaks, meteor trails) to yield absolute intensities to a ±10% accuracy.

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