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Hydra Modifications for WIYN (1Sep94) (from KPNO, NOAO Newsletter No. 39, 1 September 1994) On 5 July 1994, Hydra was removed from the 4-m telescope for the last time, after serving as a workhorse instrument for the past 3 years. In the 200 nights that it was scheduled (about 1/4 of the available 4-m nights), we estimate that the instrument collected 30,000 spectra of astronomical targets (assuming about a 25% cloud-out factor). Even as this Newsletter goes to press, Hydra is undergoing a radical metamorphosis to make it optimally suited for use on the WIYN telescope. To those familiar with the instrument, the WIYN version will appear quite different from that used on the Mayall. The focal plate assembly, which includes the fiber mountings and steel focal plate on which the fibers are placed, is completely new. We are replacing the stepped focal plate with a warpable plate to take advantage of the concentricity between the WIYN exit pupil and focal surface radius of curvature. We expect the new fiber pivot guards will eliminate the occasional fiber to fiber tangling which has caused a few wake up calls late at night. The blue fiber cable will have 3 arcsecond fibers while the red cable has a fiber aperture of 2 arcseconds. The calibration screen has been replaced with a screen located above the fiber positioner and the number of hollow cathode tubes has been increased to improve the flux level. Guiding of the telescope will also now utilize the Field Orientation Probes themselves instead of independent offset guide probes. An artist's rendition of the new instrument is shown in the figure. [Figure not included] The Bench Spectrograph is undergoing slight modifications which include: a) a stiffer camera axis to improve wavelength setup reliability; b) new grating cells for the available gratings; and c) a new dedicated CCD and controller (ARCON). The new CCD will be a SITe (formerly Tektronix) 2048 device similar to T2KB. We have also made a concerted effort to eliminate potential background light sources from the spectrograph room at WIYN, which should improve the quality of low signal data over that obtained at the 4-m. Commissioning of the new Hydra at WIYN will commence this fall and continue through the winter. If all goes well, we expect to release Hydra for shared-risk science observing in the spring of 1995. We look forward to a long and very productive tenure at WIYN. Sam Barden, Taft Armandroff
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