Long-Slit Ultraviolet Spectroscopy of Comet Austin (1990 V)

Abstract

A long-slit far-ultraviolet spectrum (1250-1850 Å) of Comet Austin (1990 V) was obtained from a sounding rocket experiment launched on 21 April 1990. Emissions of OI, CI, SI, and CO were detected during the 270 sec of data acquisition. The spectral resolution was 5.5 Å, while the spatial resolution was limited by pointing jitter to ∼30 arcsec. The spatial profiles of the carbon and oxygen emissions show narrow enhancements which are suggestive of a cometary outburst which occurred 15-20 hr before the observation. The spatial distribution of the atomic carbon is similar to that measured during two observations of Comet P/Halley (1986 III) and, as in the case of Halley, is not well matched by current models of CO photodissociation. The CO profile, for cometocentric distances greater than 104 km, is that of a parent molecule evaporating directly from the nucleus with a production rate of 4.0 ± 1.3 × 1027 molecules sec-1. The Oi λ1304 emission, also similar in spatial distribution to that observed in Halley, includes a contribution due to Bowen fluorescence induced by solar Hi Lyman-β, and its distribution can be understood as that due to the photodissociation of H2O, with a production rate of 6.2 ± 3.3 × 1028 molecules sec-1. The abundance of CO, relative to water, is 6.5 ± 4.0%. The spatial profile of Si λ1814 was also obtained, and is consistent with that of a daughter product of short-lived species such as CS2 and H2S, with a total production rate of 6.0 ± 1.9 × 1026 molecules sec-1.