COMPARISON OF WATER PRODUCTION-RATES FROM UV SPECTROSCOPY AND VISUAL MAGNITUDES FOR SOME RECENT COMETS

The temporal evolution of comets Bradfield (1987 XXIX), P/Tempel 2 (1987g), Wilson (1987 VII), and P/Halley (1986 III), as derived from the ultraviolet and visible coma emissions observed with the International Ultraviolet Explorer (IUE), are compared with the visual lightcurves from magnitudes reported in the IAU circulars. Water production rates derived from visual magnitudes using the method of Newburn agree with OH-derived rates to first order, but are sometimes displaced or fail to show the same pre/postperihelion asymmetry. Some correlation with gas-to-dust ratio is noted. The agreement is best for P/Tempel 2, a relatively dust-free comet. Lightcurves from the IUE fine error sensor (FES) are generally in agreement with the curves based on reported total visual magnitude, despite the simple equation used to extrapolate from the small effective aperture of the FES (∼18″) to an effective total magnitude. © 1990.