WAYELENGTH OFFSETS AMONG INTERNAt LAMPS AND EXTERNAL SOURCES

M. SIRK and R. BOHLIN
SPACE TELESCOPE SCIENCE INSTITUTE

Instrument Science Report CAL/FOS—041
April 1987


A bstract

Qffsets between spectral features from the internal direct PtCrNe and
an external PtCrNe calibration lamp are determined from G270H spectra
for both Digicons and show an offset of less than 0.1 diode on the
blue side and a non-constant offset with a range of 0.35 diode on the
red side. Otfsets between the crossstrapped and direct internal lampe
vary with wavelength over a range of about 0.2 diode on both
eides. There is evidence that the amount of offset as a function of
wavelength is independent of the choice of apertures. A calibration
test procedure to establish tlie repeatability of the
internal/external offsets as a function of diode number for all
dispersers is outlined in § IV. II these offsets repeat and can be
reliably calibrated, tbe accuracy of FOS wavelength scales should be
an order of magnitude better, in the range of 0.03 diode.