Fabry-perot for airborne infrared astronomy and the [Si II] emission from the galactic center

A Fabry-Perot spectrometer for infrared astronomy was built for and used on NASA's Kuiper Airborne Observatory. This instrument produces very high resolution spectra between 15 and 50 μm. The Fabry-Perot uses free-standing metal mesh for its optical resonant cavity and servo-controlled motors to vary the transmitted wavelengths. The fine-structure lines of [S III] to 18.71 μm (M42) and 33.482 μm (M17) in Galactic HII regions and [Si II] at 34.816 μm (S 106) in a photodissociation region (PDR) were observed with the Fabry-Perot. The distribution of the [Si II] 34.816-μm emission from within 5 parsecs of the Galactic center is measured with the Cornell high-resolution grating spectrometer, which is also used as the order-sorter for the Fabry-Perot. The gas-phase abundance of silicon within the neutral gas ring surrounding the Galactic center is 4.5 x 10-6. The Si II 34.8-μm/O I 63.2-μm line ratio is independent of the emitting region temperature and density, so the relative abundance of Si II to O I may be determined directly