OPTOPUS observations of Halley’s comet

The multiobject spectrograph OPTOPUS, for use at the 3.6-m ESO telescope with the CCD detector, is described, and preliminary results of spectra obtained in December 1985 of selected regions in the coma of Halley's comet are presented. The instrument's 54 separately cabled optical fibers, whose input ends are located in the focal plane by connectors plugged into drilled starplates, enable light to be guided from freely distributed points in a 33 arcmin zone of the Cassegrain focal plane, to a common slit. The spectra show the presence of a very faint continuum, due to the scattering of solar line photons in the inner region of the coma, on which is superimposed the bright emission bands of molecules such as CN, C2, C3, and NH2. The spectra also indicate that the brightness decrease of molecular bands as a function of the projected radial distance is not the same for different molecules.
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ESO