First observations with the LLNL optical imaging Fourier Transform Spectrometer.

We present the results of the first observing run with an optical imaging Fourier transform spectrometer (FTS). We have designed and fabricated this FTS for low-background astronomical use as a testbed for a proposed imaging FTS for the Next Generation Space Telescope (NGST). The relatively low background in the optical allows us to mimic the long dwell, step-scan operation of the proposed infrared NGST FTS. In this first data set, we have demonstrated the operation of the system as a multi-band camera and as a medium-resolution 3D spectrometer. Our testbed FTS reflects our current design for the NGST FTS (IFIRS). It is a four-port (two input, two output) Michelson interferometer with two 45 degree, self-compensating beamsplitters and cube-corner retro-reflectors. This system was taken to the 1.5-m McMath-Pierce Solar Observatory (MPSO) in March 1999. MPSO provides a good facility for prototyping astronomical instruments with a horizontal focal plane projected onto a (de)rotating table. We collected data from one output port with an off-the-shelf PixelVision CCD camera with a 1024x1024, thinned SITe chip thermoelectrically cooled to 235K. Our final platescale was about 0.5 arcsec/pixel with an unvignetted field of about 4x4 arcmin. We collected imaging spectroscopy with resolutions of a few to 500 of well-known objects including globular clusters, open clusters, spiral galaxies, elliptical galaxies, and nebular regions. We describe our data reduction procedures with emphasis on the unique aspects of imaging FTS data. We present color-magnitude diagrams of star clusters to demonstrate the utility of the imaging FTS as a camera and compare the signal-to-noise performance with theoretical models and filter-based camera performance. Finally, we present datacubes demonstrating the ability of the imaging FTS to yield ``a spectrum for every pixel''