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We have designed and constructed a fiber optical coupler for an existing low resolution (120 Angstroms/mm) Cassegrain spectrograph. The coupler contains a beveled plug which acts as the decker of a conventional spectrograph. The fiber, which projects through the plug, acts as the slit. The coupler also contains guiding and reference source optics. The coupler and spectrograph will be used with the College of Charleston's 16 inch telescope and an SBIG ST-6 CCD camera to conduct a radial velocity search for short period binaries from among a sample of cool, x-ray emitting stars. One advantage of using a coupler for this work is that the spectrograph can be removed from the telescope allowing it to be housed in an environmentally controlled area. This reduces spectral shifts due to flexure and to changes in the ambient temperature. Another advantage is that the fiber provides excellent azimuthal scrambling of the incident light. In practice, this means that the image can wander about on the input end of the fiber with little effect on the output light cone. A third consideration is that the coupler design allows quick shifts between spectrographic and photometric instrumentation. This is particularly important for small college observatories with limited personnel resources.
This work has been supported by a NASA South Carolina Space Grant Consortium grant, an AAS administered NSF Research Experience for Undergraduates award, and by a grant from the Research Corporation.
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