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D. R. Andersen (Penn State University), M. A. Bershady (UW-Madison), L. W. Ramsey (Penn State University)
We describe the Formated Field Unit (FFU) under construction at Penn State University for the 9m Hobby-Eberly Telescope's (HET) Medium Resolution Spectrograph (MRS): Spider. This FFU is an array of fiber optic cables formatted optimally to spectrally image single, extended, axi-symmetric sources, such as galaxies and planetary nebulae. The FFU consists of four, 15 arcsecond long slits with a common center but at four position angles (like an aserisk, or spider). Each slit is sampled by 1 arcsec diameter fibers (200 \mum), spaced 1.3 arcsec apart. Spider will be installed during the commissioning phase of the MRS (mid 1999). This fiber-fed echelle spectrograph has a resolution of 10,900 for a 1 arcsec aperture, and initial spectral coverage from 0.5-0.95 \mum in a red beam. The large telescope aperture and fiber size of Spider yields large étendue (50 m2 arcsec2). There are currently no fiber arrays either planned or in existence which are comparable. Hence this FFU fills a niche for moderate resolution spectroscopy at low surface-brightness. The FFU is expected to reach a limiting surface-brightness in V of 22 at S/N = 10 per spectral resolution element per fiber at R = 10,900 in one hour; this assumes a peak throughput of 15% for the HET plus MRS system. In this presentation we outline the expected performance, design and construction progress to date, and our characterization of fiber packing quality and focal ratio degradation from test arrays. We also demonstrate how the Spider FFU can be used for kinematic studies nearby and moderately distant galaxies. The fiber array will be capable of delivering simultaneous rotation curves and disk velocity dispersions over a range of look-back times. This research is supported by NSF/AST 96-18849.