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M. J. Wolf (U. Texas), G. J. Hill (McDonald Obs.), W. Mitsch (Uni-Sternwarte, Munich), W. Altmann (Konstructionsbuero W. Altmann)
The Low Resolution Spectrograph (LRS) will be the first facility instrument on the 9.2 m Hobby-Eberly Telescope (HET). The LRS has three modes: imaging, long-slit spectroscopy and multi-object spectroscopy (MOS). We present the design of the LRS MOS unit which provides 13 slitlets, each 1.5-arcsec. by 15 arcsec., on 20 arcsec. centers within the 4 arcmin. (50 mm) field of view of the HET. This unit was chosen over the more conventional slit masks due to the queue scheduling of the HET, and the remote location of the instrument, at prime focus.
The MOS unit has miniature mechanisms based on custom crossed-roller stages and 0.25 mm pitch lead-screws. 10 mm diameter geared stepper motors drive the 13 axes at 0.8 micron per step. The precision of the mechanism is far greater than required by the HET plate scale of 205 microns per arcsec., but results in a robust unit. The total cost of the MOS unit was about $40,000. The unit will be available for inspection.