The Death of Comet Tabur 1996 Q1: The Tail without the Comet

Abstract

After a normal brightness increase, Comet Tabur 1996 Q1 showed a remarkable photometric behavior by rapidly fading in late October 1996. In this paper we analyze three CCD images of the remnant dust tail observed during the fading of the comet around perihelion and model them by means of the inverse dust tail model (M. Fulle, 1989,Astron. Astrophys.217, 283–297). Assuming hemispherical sunward dust emission from the nucleus, satisfactory fits of the observed tail brightness distribution, turning axis and temporal fading allow us to conclude that only dust was observed, and contamination by gas and/or ions in the images is negligible. The model results include the temporal variation of the dust ejection velocity, the size distribution and dust mass loss rate. These values show a strong correlation during fading with strong drops consistent with the comet's deactivation. In particular, the slow increase of the dust mass loss rate in September and its low absolute values allow us to exclude outbursts preceding fading and to exclude that the disappearance was due to a complete nucleus disruption. In this case, the nucleus mean radius should have been no more than 350 m (for a nucleus bulk density of 100 kg m−3), which seems inconsistent with the observed water loss rate. A probable explanation of the comet fading is that the comet nucleus deactivation was due either to seasonal effects, putting all active areas in permanently night sides, or to the complete end of the whole nucleus surface activity (possibly due either to nucleus mantling or to the end of the ice reservoirs).