A single-photon counting astronomical spectrophotometer.
A spectrophotometer originally used with current measuring photometry has been modified to take advantage of the increased information rate obtainable through single-photon counting. Through careful guiding, relative wavelength displacements between successive scans can be kept to 0 +/- 0.1 A. In one test, shot noise appears to dominate for count rates less than l0(4)/see on photometric nights. Used with the 208-cm Struve reflector at McDonald Observatory, objects as faint as m(p) = 15.3 have been successfully observed with a slit width of 150 A, corresponding to a resolution of 40. Objects as bright as V = 0.0 are observed with integration times of 1 sec and a slit width of 0.1 A, corresponding to a resolution of 50,000.
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