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Hubble Space Telescope
GHRS Instrument Science Report 055

GHRS Instrument Science Report 055

"Line Spread Functions for GHRS Spectra with the LSA (Pre-COSTAR)

Ronald L. Gilliland and Stephen J. Hulbert

Abstract excerpted from the report:

The spherically aberrated point spread function of the HST
provides input to the 2.0" LSA that is characterized by a
sharp core and broad wings. The extended PSF wings contribute
to a significant resolution degradation for spectra acquired through
the LSA.  The 0.25" SSA is matched in size to the spectroscopic
resolution element; spectra taken in the SSA suffer a loss of 
throughput, but no significant resolution degradation. Through
comparing spectra of a sharp-lined star acquired through both the
LSA and SSA it is possible to derive the added line spread 
function (LSF) blurring of the LSA relative to the SSA. We report
on empirical determination of the LSA spectral resolution degradation
for three different wavelengths and four spectral elements of the