Detailed Characterization of Low Activity Comet 49P/Arend-Rigaux

Abstract

Comet 49P/Arend-Rigaux is a well known low-activity Jupiter Family comet. Despite the low activity, wehave witnessed outgassing activity in 1992, 2004, and 2012. In 2012 a broad tail-like feature (PA∼270°,∼2.3×10^5 km) and a narrow jet-like feature (PA∼180°,∼9.3×10^4 km) were seen simultaneously. UsingFinson-Probstein (FP) dust dynamical models we determine: the grain sizes released in each event; the durationof activity; when the activity peaked; and the velocity of the dust particles, allowing us to make comparisonsbetween the events. We find that the tail feature in 2012 is similar to the tail in 1992 with large grains (40-4000μm) peaking in activity around perihelion with a long duration of outgassing greater than 150 days. The jetfeature from 2012, however, is more similar to the 2004 event which we model with small grains (1-8 microns) with a short duration of activity on the order of one month. The main difference between these two features is that the2004 event occurs prior to perihelion, while the 2012 event is post-perihelion. We use the grain sizes from theFP models to constrain ice sublimation models. Between 1985 and 2018 we cover six apparitions with 26 nightsof our own observations, data from the literature, and data from the Minor Planet Center, which together, allowus to model the heliocentric light curve. We find that the models are consistent with H2O ice sublimation as thevolatile responsible for driving activity over most of the active phases and a combination of H2O and CO2 ices are responsible for driving activity near perihelion. We measure the fractional active area over time for H2O anddiscover that the activity decreases from an average active area of∼3% to ∼0.2%. This clear secular decreasein activity implies that the comet is becoming depleted of volatiles and is in the process of transitioning to eithera dormant or dead state.