Hydra CTIO, an upgraded version of the Hydra WIYN fiber positioner, is being constructed by the Instrument Projects Group in Tucson for use on the Blanco telescope. To prepare for Hydra's arrival, CTIO is installing a new R-C field corrector with atmospheric dispersion compensation on the telescope, and completely rebuilding the old Argus bench mounted spectrograph, a level of effort comparable to the building of Hydra itself.
Hydra will have two sets of 138 independently positionable fibers, 1.3" and 2.0" (200 and 300 microns) in diameter. Both the fibers and the corrector have been designed so that the system will be efficient over the widest possible wavelength range. Losses in the corrector and fibers are expected to be small at all wavelengths longward of 4000Å. Fiber losses will decrease the throughput in the UV, but we expect the system will be useful to 3350Å, the short-wavelength cutoff of the corrector. The fibers are also believed to transmit well at wavelengths of up to 2 µm, leaving the possibility open for a future upgrade of Hydra CTIO for use in the near IR.
The Hydra positioner is scheduled to arrive at CTIO on 1 October 1998, by which time the new corrector will have been installed and characterized. The system will be commissioned during October-December with the goal of having the instrument available for shared risk observing during the first semester of 1999 and routine observing thereafter.
Commissioning of Hydra CTIO, installation of the new corrector, a scheduled biennial 4-m aluminization, plus upgrades to the 4-m telescope's encoders and servo motors means that the demands for engineering time on the Blanco are unusually heavy during second semester 1998. We ask users to bear with us as we feel the result will be a much improved telescope and instrument package.
Observers contemplating shared risk use of Hydra CTIO during first semester 1999 should consult the existing Hydra WIYN and Argus documentation in preparing their proposals. Hydra CTIO's user interface will be similar to that of Hydra WIYN so the instruments will appear much the same to the observer. However, Hydra CTIO is expected to position fibers several times faster and to greater accuracy.
The new spectrograph will be optically quite different from the one used in Argus, but the same gratings will be used, so the resolutions and coverage available on Hydra will be approximately the same as those listed in the Argus documentation.
Tom Ingerson (tingerson@noao.edu)