RITMOS: a micromirror-based multi-object spectrometer

Abstract

The Rochester Institute of Technology Multi-Object Spectrometer (RITMOS) utilizes a Texas Instruments Digital Micromirror Device (DMD) for target selection, instead of the fiber bundles or customized slit masks normally used in multi-object spectroscopy. The DMD, which sits at the telescope focal plane, is an 848 x 600 array of 17 micron square mirrors that can individually deflect incident light into one of two output paths: an imaging path or a spectroscopy path. In standard operation, all light is deflected towards the imaging path, consisting of an Offner relay which reimages the DMD onto a CCD detector. The locations of spectroscopic targets are then noted, and the micromirrors corresponding to these targets are then deflected towards the spectroscopy path. This path utilizes a 1200 l/mm transmission grating to disperse images of the micromirror pattern onto a second CCD detector. The spectroscopic parameters (e.g., 0.66 Å/pixel dispersion for a 13.5 micron/pixel detector) were chosen for MK spectral classification. Among the benefits of replacing a fiber bundle or custom slit mask with a DMD are the latter's instantaneous reconfigurability and its aptitude for the study of compact fields. RITMOS is thus suited towards spectral classification surveys of star clusters. We present a description of the instrument, details of its design, and initial measurements, including multi-object stellar spectra.