Far-ultraviolet background observations at high galactic latitude. II - Diffuse emission

Abstract

A single spectrum, of extremely long integration time, is used to place stringent new limits on the diffuse far-UV background in the 500-1200 A region. This spectrum, obtained in the vicinity of the North Galactic Pole with the Voyager 2 UV spectrometer, can be explained solely on the basis of resonant scattering from interplanetary H I and He I. Limits on any additional sources of sky background radiation corresponding to 100-200 photons/sq cm per sec/sr per A for continuum emission and 6000 photons/sq cm per sec/sr for line emission are demonstrated. Comparisons of these upper limits with existing measurements and various potential source mechanisms are discussed. The first detection of resonantly scattered interplanetary H I Ly-gamma (973 A) emission is reported.