Ground-based telescopes require useful and productive instruments to stay relevant in astronomy. The Kitt Peak Ohio State Multi Object Spectrograph (KOSMOS), originally on the Kitt Peak National Observatory (KPNO) 4-meter Mayall Telescope, is a long-slit and multi-object, low-resolution spectrograph. KOSMOS was acquired by the Astrophysical Research Consortium (ARC) for the Apache Point Observatory (APO) ARC 3.5m telescope, implemented redesigns to the instrument, and renamed KOSMOS II. The instrument was integrated into the ARC 3.5m's operational environment by adding a Nasmyth port adapter, a cart with truss for mechanical support, and telescope user interface (TUI) software. Upgrades include slit-viewing guiding, internal calibration lamps, heat exhaust, and a new cryostat. Since 2021, KOSMOS II has proven capable of the high-throughput, low-resolution spectroscopy required by the ARC 3.5m user community. This paper describes the design updates and revisions made to the instrument along with measurements of its performance.
KOSMOS is a low-resolution, long-slit, optical spectrograph that has been upgraded at the University of Washington for its move from Kitt Peak National Observatory’s Mayall 4-m telescope to the Apache Point Observatory’s ARC 3.5-m telescope. One of the additions to KOSMOS is a slitviewer, which requires the fabrication of reflective slits, as KOSMOS previously used matte slits machined via wire electrical discharge machining. We explore an innovative method of slit fabrication using nanofabrication methods and compare the slit edge roughness, width uniformity, and the resulting scattering of the new fabricated slits to the original slits. We find the kerf surface of the chemically etched reflective silicon slits are generally smoother than the machined matte slits, with an upper limit average roughness of 0.42 ± 0.03 μm versus 1.06 ± 0.04 μm, respectively. The etched slits have width standard deviations of 6 ± 3 μm versus 10 ± 6 μm, respectively. The scattering for the chemically etched slits is higher than that of the machined slits, showing that the reflectivity is the major contributor to scattering, not the roughness. This scattering, however, can be effectively reduced to zero with proper background subtraction. As slit widths increase, scattering increases for both types of slits, as expected. Future work will consist of testing and comparing the throughput and spectrophotometric data quality of these nanofabricated slits to the machined slits with on-sky data, in addition to making the etched slits more robust against breakage and finalizing the slit manufacturing process.
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