FOS Instrument Science Report #106

"PRE-COSTAR FOS APERTURE TRANSMISSIONS FOR POINT SOURCES and SURFACE BRIGHTNESS
OF DIFFUSE SOURCES" by Ralph Bohlin

Abstract excerpted from the report:
	The FOS absolute sensitivities are determined by observations of 
	standard stars in the 4.3" acquisition aperture.  For estimates of
	absolute fluxes of point sources that are observed in smaller apertures,
	the apparent, measured transmission of the smaller aperture relative
	to the 4.3" aperture is required.  The proposal ID 4211 was designed
	to extend our knowledge of these aperture corrections and to verify
	the stability of the throughput relative to earlier measurements by 
	propid 3106 in 1991.  Despite the lack of a theoretical explanation,
	the data demonstrate that the aperture corrections depend on the 
	detector and grating and, therefore, differ from the true transmission
	of the aperture, which is a function of only the aperture size and the
	PSF at the relevant wavelength.

	The formula for computing of the specific intensity of sources of 
	diffuse surface brightness depends on the absolute fractional 
	transmission of the 4.3" aperture for a point source but NOT on the
	aperture correction for a smaller observation aperture.


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