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Hubble Space Telescope
GHRS Instrument Science Report 039

GHRS Instrument Science Report 039

"The accuracy and repeatability of pipeline GHRS wavelength calibration"
6/92

J.R. Walsh

Abstract excerpted from the report:

The wavelengths of Pt-Ne lines measured in GHRS wavelength calibration data
have been compared with the tabulated wavelengths of the lines to derive the
absolute accuracy of the routine pipeline calibration. For the first order 
gratings the maximum value of the observed-expected wavelength averaged over
each range was a 0.09A. However the difference between the measured and
standard wavelengths varies little between the individual ranges of each
grating and with time, based on two sets of identical calibration data taken
in January and May 1992. The reproducibility of the calibration implies that
with a simple shift applied to the wavelength scale an accuracy of ~0.02A is
achievable.

Analysis of the measured wavelengths of lines in one wavelength range of
Echelle-B over a period of 1.3 days in January 1992 shows that routine 
accuracy of 0.03A is achieved by the pipeline calibration, and as for the 
first order gratings this offset is rather stable. However there is still
some systematic drift of the wavelengths which can be correlated with
temperature, implying that further improvements in pipeline calibration could
lead to greater accuracy.