Hyperspectral Imaging: Wide‐Area Spectrophotometry Using a Liquid‐Crystal Tunable Filter

Abstract

ABSTRACTThis paper reports on the use of a tunable, liquid‐crystal filter to obtain simultaneous, low‐resolution spectrophotometry of multiple stars within a moderately crowded field. The filter is electronically tunable to any wavelength in the range from 400 to 720 nm with a nominal passband of 10 nm FWHM. In order to evaluate the performance of this filter, the central region of the Jewel Box cluster, NGC 4755, was repeatedly imaged as the filter’s central wavelength was stepped from 435 to 720 nm in successive exposures. A spectrum for each of five brighter stars in the cluster field was then reconstructed from the stack of images. Differential corrections for each frame were determined by using a standard spectral scan for one of the stars in the field with a known spectral type (the “reference star”). Dereddened spectra of the other stars in the field were then constructed with accuracy only limited by the match between the reference and standard star spectra, and uncertainties in variable reddening across the cluster. This technique allows multiobject spectroscopy to be obtained in potentially very crowded stellar fields using common photometric reduction techniques—namely, PSF fitting.