4 - The Extreme Ultraviolet Explorer and ALEXIS sky surveys

Summary

The Extreme Ultraviolet Explorer

S. Bowyer and his team at the University of California, Berkeley, the pioneers of EUV astronomy, originally proposed the Extreme Ultraviolet Explorer (EUVE) mission to NASA in 1975. Selected for development in 1976, it was eventually launched in June 1992, almost exactly two years after ROSAT. The science payload was developed and built by the Space Sciences Laboratory and Center for EUV Astrophysics of the University of California at Berkeley. Like the WFC, a principal aim of EUVE was to survey the sky at EUV wavelengths and to produce a catalogue of sources. However, the two missions differed in several respects. While the WFC had a filter complement allowing it to observe at the longer wavelengths of the EUV band (P1 and P2 filters), the survey was only conducted at the shorter wavelengths from 60 Å to ≈200 Å. By contrast, the EUVE survey was carried out in four separate wavelength ranges, extending out to ≈800 Å. In addition, EUVE carried on board a spectrometer for pointed observations following the survey phase of the mission. The spectrometer will be discussed in detail in chapter 6, but half the effective area of its telescope was utilised for a deep survey imager, giving exposure times significantly larger than either the WFC or EUVE all-sky surveys but over a restricted region of sky. The following sections include a detailed description of the payload components drawn from several papers in the scientific literature (see e.g. Bowyer and Malina 1991a,b).