HexPak and GradPak: Variable-Scale Dual-Head IFUs for the WIYN 3.5m Telescope Bench Spectrograph

Type Conference Paper
Names Corey Wood, M. A. Bershady, A. Eigenbrot, S. A. Buckley, J. S. Gallagher, E. Hooper, A. Sheinis, M. P. Smith, M. J. Wolf
Proceedings Title Bulletin of the American Astronomical Society
Conference Name AAS Meeting #221, #345.06
Date January 1, 2013
Short Title HexPak and GradPak
URL http://adsabs.org/2013AAS.22134506W
Library Catalog labs.adsabs.harvard.edu
Abstract We present two new fiber integral field units (IFUs) -- HexPak and GradPak -- for the WIYN 3.5m Telescope Nasmyth focus and Bench Spectrograph. We describe their design, construction, and laboratory performance. These are the first IFUs to provide formatted fiber integral field spectroscopy with simultaneous sampling of varying angular scales. HexPak and GradPak are in a single cable with a dual-head design, permitting easy switching between the two different IFU heads on the telescope. Switching between the two heads requires no change to the spectrograph: the two heads feed a shared variable-width double-slit. Each IFU head is comprised of a fixed arrangement of fibers with a range of fiber diameters. The layout and diameters of the fibers within each array are scientifically-driven for observations of galaxies: HexPak is designed to observe face-on spiral or spheroidal galaxies while GradPak is optimized for edge-on studies of galaxy disks. HexPak is a hexagonal array of 2.8 arcsec fibers subtending a 40.9 arcsec diameter, with a high-resolution circular core of 0.94 arcsec fibers subtending 6 arcsec diameter. GradPak is a 39 by 55 arcsec rectangular array with rows of fibers of increasing diameter from angular scales from 1.9 arcsec to 5.6 arcsec across the array. The varying fiber diameters of these IFU heads allows for adequate sampling of light profile gradients while maintaining the photon limit at different scales. We report laboratory tests of the throughput and focal ratio degradation properties of each IFU.
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