Far-ultraviolet spectral images of comet Halley from sounding rockets

Abstract

Wide-field ultraviolet imagery of comets provides a useful means of determining such fundamental parameters as production rates, lifetimes and outflow velocities of daughter photodissociation products in the coma. Far-ultraviolet imagery has been used to measure the production rates and outflow characteristics of hydrogen for comets Bennett¹, Kohoutek^2,3 and West^4,5, for C and O in comet Kohoutek⁶, and for C, S and CS in comet West⁷. Ultraviolet spectroscopy has also revealed the presence of C⁺ ions and CO molecules⁸ in comet West. Other comets have been observed spectroscopically in the ultraviolet from the International Ultraviolet Explorer (IUE) spacecraft⁹. Here we present far-ultraviolet images of comet Halley obtained from sounding rockets launched from White Sands Missile Range, New Mexico, on 24 February and 13 March 1986. We gained direct electrographic images of the hydrogen coma of the comet at the Lyman-α wavelength (1,216 Å), and objective spectra containing images of the coma at the oxygen (1,304 Å), carbon (1,561 and 1,657 Å) and sulphur (1,814 Å) resonance multiplets. Analysis of the Lyman-α images yields hydrogen atom production rates of l.9 × 10³⁰ s⁻¹ and 1.4 × 10³⁰ s⁻¹ for the two observations. Images of oxygen, carbon and sulphur emissions obtained with the objective grating spectrograph are presented for the first set of observations and preliminary production rates are derived for these elements.