FOS Instrument Science Report #114

"Scattered Light in the FOS:  An Assessment Using Science Data"
by Michael R. Rosa

Abstract excerpted from the report:
	The Faint Object Spectograph (FOS) uses a truly one-dimensional
	detector and so source and the background signal-sky and internal-
	usually cannot be observed strictly simultaneously.  In this analysis
	some 360 individual exposures of a large variety of target types and
	magnitudes have been inspected in tow FOS modes that do not provide
	simultaneous background recording, namely BLUE side detector with
	grating G130H and AMBER detector with grating G780H. Residual 
	counts in portions of diode array that cover wavelength ranges with 
	near zero sensitivity seem to originate from at least two sources.

	The charged particle induced background is usually about 30% stronger 
	than predicted by the calibration currently in use in the standard
	pipeline reduction.  In addition, bright red targets show the 
	presence of a considerable amount of diffuse scattered light in 
	the spectograph.  The data suggest that mirror-imaged ghost spectra
	are of no concern.  an empirical model incorporating both of the
	former cases is show to match the observational data.  Prescriptions
	for recalibration of FOS BLUE, G130H data are given and the impact on
	the final calibrated fluxes demonstrated.




For more information, please contact the above authors.