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Session 41 - Visible & UV Telescopes.
Display session, Thursday, January 08
Exhibit Hall,
We describe two fiber-optical arrays (IFUs) under construction at Penn State University for the 9m Hobby-Eberly Telescope's (HET) Medium Resolution Spectrograph (MRS). These arrays optimize integral-field spectroscopy for kinematic studies of individual, nearby and moderately distant galaxies, but will have more general application to moderate spectral resolution studies of extended sources at low surface-brightness. Once in place, the fiber arrays will be capable of delivering simultaneous rotation curve and disk velocity dispersion measurements over a range of look-back times. These measurements can be used to separately estimate the disk mass and total mass of galaxies. Such surveys would have important implications for the nature of dark matter. One array spans over 30 arcsec using 2 arcsec (400 \mum) fibers to densely sample slits at 4 position angles at resolution from 5500 to 11000. The second array spans 15 arcsec using 1 arcsec fibers to densely sample a core area of \sim60 arcsec^2 at resolution of 11000 to 14500. In contrast, fiber arrays planned for other 10m-class telescopes generally are optimized for smaller areas and higher angular resolution, but are commensurately limited to higher surface-brightness at fixed spectral resolution. Our 400 micron array will be installed during the commissioning phase of the MRS when this fiber-fed echelle spectrograph will have a resolution of 10,900 for a 1 arcsec slit and spectral coverage from 0.5-0.95 \mum in a red beam. In this presentation we outline the expected performance, design and construction progress to date, and our initial characterization of fiber packing quality and focal ratio degradation from test arrays already completed. This research is supported by NSF/AST 96-18849.
