Spectroscopy of the extreme ultraviolet background radiation

Abstract Observations in the far ultraviolet and soft x-ray bands suggest that the interstellar medium contains several components of high temperature gas and should be emitting in the extreme ultraviolet. Indeed diffuse radiation has been detected in the extreme ultraviolet with photometric instruments, but no spectral measurements exist below 520A. We have designed a unique grazing incidence spectrometer to study the diffuse emission between 80 and 650A with 10 to 20A resolution. The instrument was launched on a Black Brant sounding rocket from White Sands Missile Range on April 22, 1986. Our preliminary analysis shows the expected geocoronal and interplanetary HeI 584A emission, and possibly other features which may originate in the hot ionized interstellar gas. Flux limits to these possible emission lines are compatible with previous broad band measurements.