The visual light curve of C/1995 O1 (Hale-Bopp) from discovery to late 1997

Abstract

We present a light curve of C/1995 O1 (Hale-Bopp) compiled from more than 3000 visual observations of the comet made by members of the The Astronomer Group world-wide. These observations cover the period from discovery through to the end of 1997. The light curve shows that the rate of brightening of the comet varied widely at different times, with rapid rates of brightening at high heliocentric distance pre-perhelion and a comparably rapid post-perihelion fade. There is no evidence that the comet was suffering a large photometric outburst when first discovered, although a small outburst can be identified at perihelion. At least five difficult brightening regimes can be identified in the light curve between discovery and perihelion. From 2.5 AU to perihelion the rate of brightening with decreasing heliocentric distance was typical for 'fairly' new comets (n ~ 3.5, where 'n' is the power law exponent of the heliocentric distance), although this was preceded by a period of very slow brightening with n ~ 1 from r ~ 4.0 AU to r ~ 2.8 AU and followed by an initially more rapid brightening which appears to be related to the on-set of rapid water sublimation activity. We derive the light curve parameters at different stages of the comet's apparition.