The Fan Mountain Observatory Bench Spectrograph

Abstract

The Bench Spectrograph at the University of Virginia's Fan Mountain Observatory is being built for use on the facility's primary research telescope, the 1-meter astrometric reflector. The spectrograph is designed for initial use as a dedicated instrument to collect moderate-resolution (10 km/s^-1) spectra of candidate K giant stars for the Grid Giant Star Survey (GGSS), which is a program to identify stars for the Astrometric Grid of NASA's Space Interferometry Mission (SIM). The spectrograph is a single-object, fiber-fed design built with off-the-shelf optics at modest cost. The primary optics are transmissive, and a 1200 line/mm reflectance grating is used to provide a resolving power of R ~ 2000 at &lambda; ~ 500 nm. Because the GGSS candidate sample is extensive, bright (V &lt; 13), and uniformly distributed over the sky, a fiber-fed design was selected to provide maximal spectral stability and uniformity (to obtain high quality spectra, suitable for luminosity classification, abundance analysis, and radial velocity measurement) while optimizing observing efficiency. Although the primary wavelength region of interest for this application is 480-680 nm, the spectrograph will be useful throughout the optical spectrum. However, the combination of modest telescope aperture and characteristically low throughput will practically limit the spectrograph's usefulness to medium resolutions for stars brighter than about <i>V</i>~14.