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 RA/Dec = 81/+29 with an obliquity of 97 deg, 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 a 10 deg radius and a western source area at lat/long +77/245 and a 20 deg radius, 4 times 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 than that of the carbon-bearing species, implying a different driver for the polar jets such as CO or CO2. Ion tails were detected in decontaminated images from both the dust and NH filters, likely being H2O+ and OH+, respectively. We measured water production both before and after perihelion, and extrapolate peak water production at perihelion to be about 1.0*10^29 molecules/s. We estimate 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.