An Analysis of 17 Years of Voyager Observations of the Diffuse Far-Ultraviolet Radiation Field

We have systematically reduced 17 years of data from the Voyager ultraviolet spectrometer (UVS) archives, from which we have obtained 431 spectra that place useful limits on the diffuse far-ultraviolet radiation field between 912 and 1100 Å. We observe a large range in brightnesses ranging from upper limits of 30 photons cm^-2 s^-1 sr^-1 Å^-1. The diffuse background is correlated with the integrated TD-1 flux near the line of sight but shows no correlation with N(H I). We place a 1 σ upper limit of 30 photons cm^-2 s^-1 sr^-1 Å^-1 on the level of an isotropic extragalactic continuum.

We have modeled and characterized the observed heliospheric H I and He I emission lines in the outer solar system as a function of heliospheric distance, apex angle from the direction of the inflowing interstellar wind, and time as specified by subspacecraft solar intensity. This modeling adequately reproduces observed intensities over a range of heliospheric distances of 15-50 AU, for an unrestricted range of look directions, and for a 12 year period (covering 1 solar cycle).