Implications of Initial Results from the EUVE Observatory for the FUSE EUV Spectrometer and a Possible EUVE Extended Mission

We summarize the initial scientific results from the Extreme Ultraviolet Explorer (EUVE) observatory all-sky survey and Guest Observer Programs. The initial results include the first EUVE catalog (Bowyer et al. 1993) which reports characteristics of 410 extreme ultraviolet (EUV) sources and the spectroscopic observations by guest observers of large numbers of classes of different kinds of EUV sources. We assess the implication of these initial results on the scientific objectives of the EUV spectrometer on NASA's Far Ultraviolet Spectroscopic Explorer (FUSE). The FUSE EUV spectrometer will have an order of magnitude more collecting area than the EUVE spectrometer and a resolving power several times higher. Current NASA planning anticipates a turn off of the EUVE observatory following the third year of the EUVE Guest Observer Program in 1996. A proposal is currently being prepared for NASA, in collaboration with the EUVE Users Committee, for an extension of the EUVE mission. Based on the EUVE results, we raise issues which must be taken into account in designing a science program for a possible extension of the EUVE mission such as the total number of EUV sources observable spectroscopically by EUVE. We distinguish between the science return from an EUVE extended mission and from the EUV spectrometer on FUSE given the different capabilities of the two instruments. We discuss in detail the types of scientific investigations that can be expected for cool stars, white dwarfs, extragalactic objects and cataclysmic variables. The work reported here was funded by NASA Contract NAS5--29298.