Observations of optical aurora typically require the operation of sensitive instruments at remote field sites. Absolute radiometric calibration of these devices is essential for quantitative comparison over time and with other measurements. In this study we present absolute calibration of a proton auroral photometer using star transits observed during regular data collection. This requires absolute flux spectra with sufficient resolution to account for structure in stellar H_β absorption line profiles. Several flux spectral catalogs are combined and corrected for systematic differences. The resulting estimates of instrumental sensitivity are consistent with darkroom calibration to roughly 15%.
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