Sulphur compounds in cometary IUE spectra

Abstract

Bands of S₂ have been identified in several comets including Cernis, Bowell, Churyumov-Gerasimenko, Encke, etc., covering a wide range in heliocentric distances. S₂ seems to have been present in comet Halley even from 1985 early December when it was at 1.5 AU. The authors have also tentatively identified bands of the B-X systems of the molecule SO in IRAS-Araki-Alcock in the 2200 - 2400 Å region. These bands appear to be present in comets Borrelly, Stephan-Oterma and Meier. Emissions of S+ ions, tentatively SH and several bands of CS, apart from the commonly observed ones, are evident in the spectra of comet Halley of 1986 March. Sulphur compounds are more prevalent than had been realized. Assessments of cometary dust are confused by S₂ emissions. The S₂ of comet Cernis at 3.3 AU means that the molecule is not bound in H₂O-ice, so postulated formation processes via cosmic ray or UV irradiation of ice are doubtful.