Fan Mountain Observatory


Fan Observatory Bench Optical Spectrograph (FOBOS)

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Project overview:
The Bench Spectrograph at the University of Virginia's Fan Mountain Observatory has been built for use on the facility's 40-inch astrometric reflector telescope. The spectrograph is designed for initial use as a dedicated instrument to collect moderate-resolution (~5 km/s) 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 ~ 1500 at 500 nm. Because the GGSS candidate sample is extensive, bright (V < 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 470-670 nm, the spectrograph is useful throughout the optical spectrum. However, the combination of modest telescope aperture and characteristically low throughput will practically limit the spectrograph's usefulness to moderate resolutions for stars brighter than about V ~ 14.

Questions or comments? Please e-mail Jeff Crane: