INSTRUMENT SCIENCE REPORT
	CAL/FOS 004
	
	
TITLE:	FOS Wavelength Calibration
AUTHOR:        J. Wheatley and R. Bohlin	
DATE:   5 December 1983


ABSTRACT

The dispersion relations for the eight FOS diffraction gratings are best 
approximated by 3rd degree polynomials. The RMS residual for the fits 
ranges from 0.02 pixel for grating H78 to 0.06 pixel for grating H19, 
substantially better than the spectral resolution of 1 pixel. When tbe 
2.0 arcsec (C3) aperture is used instead of the 0.1 arcsec A4, line 
blending and over exposure combine to increase the RMS residual to 
1.2 pixel. The prism has a non linear dispersion, varying from 3.8A/px 
at 1800A to 180A/px at 5500A. Wavelength as a function of pixel number for 
the prism can be approximated to an accuracy of 0.2 pixel by a fourth 
degree expansion in 1/x. Wavelength calibration data for the blue detector 
in vacuum was unintentionally omitted from the August, 1983 calibration. 
Here, we use data from the March 1983 ambient calibration to determine the 
blue dispersion constants.