Best secular light curve for comet Hale-Bopp and implications for dust production rates

We present an algorithm for reducing scatter and increasing precision in a comet light curve. We processed apparent magnitudes of comet Hale-Bopp from 17 experienced observers (archived with the International Comet Quarterly), correcting for distance from Earth and phase angle. Different observers tend to agree on the difference in magnitudes of an object at different distances, but the magnitude reported by observer is shifted relative to that of another for an object at a fixed distance. We estimated the shifts with a self-consistent statistical approach, leading to a sharper light curve and improving the precision of the measured slopes. The final secular lightcurve for Hale-Bopp ranges from -7 au (pre-perihelion) to +8 au (post-perihelion) and is the best secular light curve produced to date for this “great” comet. We discuss Hale-Bopp’s lightcurve evolution and the possible physical implications and usefulness of this light curve for comparisons with other future bright comets. We then assessed the suitability of using secular lightcurves to characterize dust production rates via the quantity "Afp" in Hale-Bopp and other dust-rich comets. We find that this method produced results congruent with more rigorously derived measurements for Hale-Bopp when it was pre-perihelion.