Scattered-Light Characteristics Of The Hubble-Space-Telescope Faint Object Spectrograph

Observations of a standard star (BD+75D325) have been used to measure the Hubble Space Telescope (HST)/Faint Object Spectrograph (FOS) scattering characteristics in the wavelength range 115 to 250 nm. Spectra of the standard star were obtained as the star was progressively offset from the optical line of sight axis of the telescope, both in the in- dispersion and cross-dispersion directions. These data have been reduced and analyzed to determine the scattering function of the telescope-spectrograph combination. Two primary results have been obtained. (1) The resulting scattering function exhibits three characteristics: (a) the inner core ((theta) < 4') is dominated by the large Point Spread Function (PSF) of the HST; (b) the outer wings of the scattering function (4' < (theta) < 32') show a (theta) -3 dependence consistent with predictions for the HST Airy disc; and (c) the wavelength dependence of this scattering function follows (lambda) -1, suggesting that the ultraviolet (UV) micro roughness contribution to the scatter is quite small, and hence the HST primary mirror is very smooth at ultraviolet wavelengths. (2) The FOS scattering contribution is limited only by grating scatter, and is consistent with pre-launch grating calibration measurements.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.