Cometary Activity at 25.7 AU: Hale-Bopp 11 Years after Perihelion

Abstract

Eleven years after its perihelion, comet C/1995 O1 (Hale-Bopp) is still active. Between 2007 October 20 and 22, we detected a diffuse coma of 180 × 103 km in diameter with a slight elongation toward the north-south direction. The integrated brightness was 20.04 mag in RC, implying Afρ=300 m and albedo × dust surface aRC=4300 km2. The coma was relatively red at V-R=0.66 mag, which is consistent with that of the dust in other comets. The observed properties and the overall fading in brightness between 10 and 26 AU follow the predicted behavior of CO-driven activity. This is the most distant cometary activity ever observed. Based on data obtained at the Siding Spring Observatory.