KPNO is pleased to announce that DensePak will be added to the NOAO WIYN instrument suite. DensePak will be used only for suitable Bright Time projects during first semester 1998.
DensePak is a fiber optic bundle that forms an array of 91 fibers in a 7 X 13 rectangle (see figure). Each fiber is 300 µm in diameter, corresponding to 3" on the sky at the Nasmyth focus of the WIYN telescope. Fiber-to-fiber spacing is 400 microns and the overall dimensions of the array are 30" X 45". The array's orientation on the sky can be selected by setting the instrument rotator to the proper offset angle. Additional fibers are offset from the array corners roughly 60" from the center to serve as sky fibers. The proximity of the sky fibers to the array may necessitate moving the telescope off target to sample the sky properly, depending on the angular size of the target. Sky fibers have the same diameter as those in the array and the "blue" fiber cable used in the Hydra MOS, though DensePak's fibers have transmission characteristics similar to the Hydra "red" fiber cable. At present, two fibers in the array are unusable (fibers 46 and 59; fibers are numbered according to their slit position at the spectrograph). In addition, the throughput of several fibers at wavelengths < 4500-5000Ĺ has been found to be substantially lower than that found for the majority of fibers in the array. Investigators proposing to use DensePak should review the relevant material at http://www.noao.edu/wiyn/obsprog.
DensePak's fiber bundle feeds the WIYN Bench Spectrograph. Therefore, users have the same spectroscopic options for DensePak as offered for Hydra (see the Hydra Users Manual at http://www.noao.edu/kpno/manuals/hydraman/hydrawiynmanual.html ). When running the spectrograph setup program, investigators should choose the blue cable to match the fiber diameter with that used in DensePak.
DensePak will have a significant impact on the planning and operation of the WIYN Queue program because DensePak and the WIYN Imager use the same instrument port. Given the delicacy of the two instruments and the amount of time necessary for an instrument change, DensePak and the imager will not be swapped during nightly operations. Furthermore, the flexibility and efficiency of the WIYN Queue during dark time are largely due to the ability to 1) switch rapidly between imaging and spectroscopy (with Hydra), and 2) match the available seeing conditions with program requirements. Nights when DensePak is mounted for use will greatly compromise many of the advantages of scheduling the NOAO WIYN time allocation in queue mode. As a result, DensePak will be restricted to use only during Bright Time for the first semester of 1998. Questions concerning DensePak may be sent to wiynq@noao.edu.
Paul Smith, for the WIYN Queue Team
(Di Harmer, Daryl Willmarth)