Multiple Object Fiber Optic Spectroscopy

We have built and operated an instrument to obtain simultaneous spectra of many objects in the field of view of the Steward Observatory 2.3m telescope. Short lengths of optical fiber are used to bring light from galaxy images at the Cassegrain focus of the telescope into a line along the spectrograph slit. This multi-fiber instrument has been dubbed the Medusa Spectrograph. This instrument is presently producing ≈ 100 spectra of galaxies down to mv ≈ 17.5 per clear night. A brief description of the instrument and observing procedure is given here. We are also developing an improved version of the instrument to record spectra at a much higher rate. In this new instrument, called the MX Spectrometer, gains in efficiency will be obtained by remotely positioning the fibers under computer control and by correctly matching the output of the fibers to the spectrograph optics. Focal ratio degradation of the f/9 beam in the fibers is suppressed by sneeding up the beam with a SELFOC lens before it enters a smaller fiber. Since the outnut of the fibers is now approximately f/4, a large collimator is placed in the spectrograph to collect the light from the fiber array at the slit. A Charge Coupled Device will replace the image tube and photographic plate detector system. The CCD will allow sky subtraction, give increased dynamic range and will provide more accurate wavelength calibration because of the fixed format detector. We are currently testing a CCD behind the image tube with the Medusa system.