The Ohio State Multi-Object Spectrograph

The Ohio State Multi-Object Spectrograph (OSMOS) is a new, wide-field imager and multi-object spectrograph for the 2.4-m Hiltner Telescope at the MDM Observatory. OSMOS has an all-refractive design that reimages a 20 arcminute diameter field-of- view onto the 4064x4064 MDM4K CCD with a plate scale of 0.273 arcseconds per pixel. 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 and consequently the instrument may be rapidly reconfigured between imaging and spectroscopic modes. At present a low-resolution triple prism (R � 60 400) and a moderate resolution VPH grism (R � 1600) are available.