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Session 34 - Real Instruments.
Display session, Tuesday, June 09
Atlas Ballroom,
The design of a long slit dual order spectrograph (DOS), being built for flight on a NASA sounding rocket by Johns Hopkins University (JHU) in the late fall -- early winter of 1999, is presented. The spectrograph is intended to survey nebular regions on intermediate angular scales in the far UV between 900 -- 1650 Åfor atomic and molecular emissions, and to study the extinction and scattering of FUV radiation by dust. It has an instantaneous field of view of \approx 4'' \times 10'', a slit limited spectral resolution of 7.7 Å\ and point source resolutions of 3'' to 5'' spatial and 3 to 3.5 Å\ spectral.
The DOS uses a concaved holographic grating with a toroidal figure in a normal incidence Rowland mount (\alpha = 0^\circ), which produces symmetric efficiency and astigmatism in the positive and negative 1st orders with low scatter. Laminar (rectangular) profiles provide a theoretical peak groove efficiency of 41% in each order for a combined groove efficiency of 82%, competitive with the 100% theoretical peak groove efficiency of a blazed grating. The use of both orders provides a valuable redundancy in a mission critical component, important in space flight applications. Our design incorporates complementary UV sensitive MCP and CCD detectors at each order to provide high dynamic range.
The DOS design is effective for imaging spectroscopy in the photon starved far UV, utilizing slow f/ratios, where low scatter, high efficiency, moderate spectral, and high spatial resolution are desired. The sounding rocket DOS is the basis of an instrument that JHU recently proposed in answer to the NASA Announcement of Opportunity for University Explorers, which we call the Nebular Explorer, (NebEx).
