Activity of comet P/Halley 23–25 March, 1986: IUE observations
A large but gradual increase in the brightness of the emission bands of comet Halley and thus in the coma abundance of OH, CS, CO 2 + and dust was observed with the International Ultraviolet Explorer (IUE) satellite from 23 to 25 March 1986. This brightness change was also monitored by the Fine Error Sensor (FES) tracking and acquisition camera at a higher temporal resolution than that of the spectrophotometric measurements. The amplitude of the increase varied among the species depending on the lifetime of the parent molecule. By comparing the FES lightcurve with the optical lightcurve measured in the light of C2 by Millis and Schleicher (1986) we can show that this increase in brightness corresponds to part of the periodic lightcurve of the comet. None of the IUE observations show evidence of the large increase in H2O reported to have occurred on March 24.7 by Weaver et al. (1986). The activity recorded between March 23 and 25 is different from the smaller and more rapid increase in brightness observed on March 18-19 also with the IUE (Feldman et al., 1986). We conclude that the activity reported here is controlled primarily by photodissociation and ionization of molecules ejected from an active area of the nucleus that rotates into the field of view of the sun approximately every 7.4 days.
Key wordsComets Spectrophotometry UV radiation
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