Coma Morphology, Numerical Modeling, and Production Rates for Comet C/Lulin (2007 N3)

Abstract

We report on narrowband photometry and extensive imaging observations of comet C/Lulin (2007 N3) obtained at Lowell Observatory during 2008 and 2009. Enhanced CN images revealed a double-corkscrew morphology with two near-polar jets oriented approximately east–west, and both CN and dust images showed nightly rotational variability and seasonal changes in bulk morphology. We determined a rotational pole direction of R.A./decl. = 81°/+29° with an obliquity of 97° and a sidereal rotation period of 41.45 ± 0.05 hr. Monte Carlo numerical modeling best replicated the observed CN features with an eastern source area at lat/long −80°/125° and an ∼10° radius and a western source area at lat/long +77°/245° and an ∼20° radius, ∼4× larger than the eastern source. An additional small, near-equatorial source was necessary to reproduce some dust features. Water morphology based on OH was quite different from that of the carbon-bearing species, implying a different driver for the polar jets such as CO or CO 2 . Ion tails were detected in decontaminated images from both the dust and NH filters, likely being H 2 O + and OH + , respectively. We measured water production both before and after perihelion and extrapolated peak water production at perihelion to be about 1.0 × 10 29 molecules s −1 . We estimated an active fraction of only 4%–5% and a nucleus radius of up to ∼8 km. Our data suggest that Lulin, defined as dynamically new in a statistical sense, behaves more like a long-period comet due to its nearly asteroidal early appearance, isolated source regions, and dust properties.