ROSAT

(roh -sat) Abbrev. for Röntgenstrahlen Satellit. A major German X-ray astronomy satellite, with UK and US collaboration, launched by a Delta II rocket into a 580 km, 53° inclination orbit in June 1990. The payload included a large (80-cm diameter) grazing incidence telescope to carry out the first deep all-sky survey in the 0.2–3 keV band. Use of such imaging optics over the first six months of the mission yielded an all-sky survey 100–1000 times deeper than those of Uhuru, Ariel V, and HEAO-1. The total number of cosmic X-ray sources detected, in this survey, some 60 000, was more than ten times the number previously recorded. A second ROSAT telescope, the Wide Field Camera (WFC), built by a consortium of UK university groups, uses grazing incidence optics at an unusually large angle and is optimized for the XUV band (0.2–0.02 keV). During the early ROSAT survey phase the WFC obtained the first all-sky survey in this energy band, detecting more than 1000 XUV sources, many being active stars or hot white dwarfs. Following the six-month survey phase, ROSAT embarked on a program of detailed observations of individual targets, chosen competitively from bids made by astronomers to the three ROSAT partners. The main spacecraft systems and three focal plane detectors (imaging proportional counter and microchannel plate arrays for the X-ray telescope plus XUV-sensitive MCP for the WFC) functioned until 1994. Thereafter observations continued with the microchannel plate array and the WFC. See also XUV astronomy.