Extreme Ultraviolet Full-Sky Survey

Description

This investigation is designed to perform a full-sky survey, searching for EUV sources. The instrument package contains four Wolter-Schwarzschild grazing-incidence telescopes (with EUV thin-film filters) to collect and to isolate radiation. The detector system for each telescope is a wedge and strip anode image converter, consisting of a microchannel plate, a wedge and strip anode, and detector amplifiers designed to produce images of sky fields in selected wavelength ranges. Three telescopes are designed to operate at right angles to the spin axis and to carry out the sky survey, with bandpass filters (tentatively) for the wavelength ranges 80 to 190 A, 170 to 330 A, and 500 to 750 A. These three telescopes point perpendicular to the earth-sun line and sweep out a great circle in the sky with each S/C revolution. As the earth moves around the sun, the great circle is shifted by 1 deg each day and so the entire celestial sphere is surveyed in 6 months. The fourth telescope points in the anti-solar direction, within the earth's shadow cone. In this limited direction, the He II 304 A background is almost completely absent, and thus higher sensitivity can be obtained for observing selected interesting objects. Spectroscopic observations of the brightest EUV sources are carried out with a resolving power of 100 from 80 to 800 A.