A Design of OMR-IFU for the 2.16m Telescope of NAOC

With the development of telescope technologies, e.g., the increase of telescope apertures and the application of adaptive optics, astronomical instruments can obtain images of higher Signal-to-Noise Ratios (SNR) in both wavelength and spatial domains. An Integral Field Spectrograph(IFS) equipped with an Integral Field Unit(IFU) has several obvious advantages in comparison with traditional slit spectrographs for certain astrophysical research fields, such as those of dense star clusters, supernova remnants, nebulae, cores of nearby galaxies, and other extended celestial objects. An OMR low-dispersion slit spectrograph on the Cassegrain focal-plane, which has been equipped on the 2.16m telescope at the Xinglong Station, National Astronomical Observatories of China (NAOC) since 1995, can be upgraded to an IFS by adopting a "lenticules+fibers" array without changing configuration. To reduce the cost, we use existing products, such as the fibers from the Polymicro Technologies Inc. and arrays of lenticules from the Adaptive Optics Associates Inc. The slit of the OMR is not very long (28.8mm, or 5.1'), so we cannot set many IFU sampling units. The IFU consists of a fore-optics system, an array of lenticules, fibers, and output microlenses. Two different IFU upgrade plans are discussed in this paper. The first has a spatial sampling scale of 1" and a field of view of 8"×8", while the second has a wider field of view (27"×31.5") but lower spatial resolution (4.5"). Because of the unchanged configuration, the new IFU will have no effect on the original function of the OMR. The IFU will be an experimental equipment. We expect it to meet the demands of some astronomical research, such as stellar kinematics in the cores of nearby galaxies, the structures of nebulae and supernova remnants, circumnuclear environments in active galactic nuclei, etc. After completion, it can be used as a routine equipment for astronomers on the 2.16m telescope.