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Hubble Space Telescope
GHRS Instrument Science Report 076

GHRS Instrument Science Report 076

"Photocathode Granularity Maps for Grating G140L of the GHRS"

A. Schultz and J. Eisenhamer

Aug 12, 1996


Maps of photocathode granularity have been created for correcting
observations made with GHRS grating G140L. These flat fields were
computed using a "tomographic" technique to separate spectrum from
granularity features using observations of BD+75D325 taken on September
22, 1995, as part of program 6209. Application of the flat field to
G140L observations taken after the 1993 HST Servicing Mission indicate
that the flat field corrects features at the 2% level for observations
with signal-to-noise greater than about 30. The technique discussed in
this ISR to create the G140L flat field can be used with care to create
flat fields for other GHRS gratings.