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Hubble Space Telescope
FOC Instrument Science Report #098

FOC Instrument Science Report #098       June 9, 1997

"FOC f/48 Spectrophotometric Calibration"
by M. Voit and R. Jedrzejewski

Abstract excerpted from the report:

This report describes the effort to calibrate the spectrophotometric
efficiency of the f/48 long-slit spectrograph. Our calibration target
was the white dwarf star LDS 749B. We stepped the target across the
slit at two different positions, three arcseconds apart, in order to
characterize the throughput as a function of target location with
respect to the slit. The target fell directly into the slit during
one exposure at each of the two slit positions, and we used these
observations to calibrate the instrument's spectrophotometric efficiency.
Vignetting affects the spectrograph's throughput at both of these
locations along the slit, and the difference in efficiency between them
agrees with the expected vignetting. Measurements of the spectrograph's
efficiency when the centroid lies slightly off the slit unexpectedly
shows greater throughput in the blue.