Hectospec, the MMT's 300 optical fiber-fed spectrograph

The Hectospec is a 300 optical fiber fed spectrograph commissioned at the MMT in the spring of 2004. In the configuration pioneered by the Autofib instrument at the Anglo-Australian Telescope, Hectospec's fiber probes are arranged in a radial fisherman on the pond geometry and held in position with small magnets. A pair of high-speed, six-axis robots move the 300 fiber buttons between observing configurations within similar to 300 s, and to an accuracy of similar to 25 mu m. The optical fibers run for 26 m between the MMT's focal surface and the bench spectrograph, operating at R similar to 1000-2000. Hectochelle, another high-dispersion bench spectrograph offering R similar to 35,000, is also available. The system throughput, including all losses in the telescope optics, fibers, and spectrograph, peaks at similar to 10% at the grating blaze in 1 '' FWHM seeing. Correcting for aperture losses at the 1.'' 5 diameter fiber entrance aperture, the system throughput peaks at similar to 17%, close to our prediction of 20%. Hectospec has proven to be a workhorse instrument at the MMT. Together, Hectospec and Hectochelle have been scheduled for 1/3 of the available nights since its commissioning. Hectospec has returned approximately 60,000 reduced spectra for 16 scientific programs during its first year of operation.