The Ohio State Multi-Object Spectrograph

The Ohio State Multi-Object Spectrograph is a new wide-field imager and multiobject spectrograph for the 2.4 m Hiltner Telescope at the MDM Observatory. OSMOS has an all-refractive design that reimages a 20' diameter field of view onto the 4064 x 4064 MDM4K CCD with a plate scale of 0.273 '' pixel(-1). Approximately an 18.5' square region of this field illuminates the detector and is available for spectroscopy, although with reduced wavelength coverage near the edges of the field. Slit masks, filters, and dispersers are all mounted in a series of six-position aperture wheels. These mechanisms rotate between positions in only a few seconds; consequently, the instrument may be rapidly reconfigured between imaging and spectroscopic modes. At present, a low-resolution triple prism (R similar to 60-400) and a moderate-resolution volume-phase holographic grism (R similar to 1600) are available.