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°, 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° radius and a western source area at lat/long +77°/245° and a ~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 than 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 extrapolate peak water production at perihelion to be about 1.0 ´ 10 29 molecules s -1 . 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.

Narrowband Observations of Comet 46P/Wirtanen During its Exceptional Apparition of 2018/19 II: Photometry, Jet Morphology, and Modeling Results

“…Furthermore, NH, C 2 , and C 3 suffer dust contamination that required photometric conditions in order to be properly analyzed, and such calibrations were too time consuming except on our dedicated nights. We made a programmatic decision to prioritize regular CN monitoring from December onwards so that we could tightly constrain the rotation period at as many epochs as possible to look for a changing rotation period; this strategy has proven to be very successful in the past, e.g., for C/2004 Q2 Machholz (Farnham et al 2007), C/2007 N3 Lulin (Bair et al 2018), 103P/Hartley 2 (Knight & Schleicher 2011;Samarasinha et al 2011), and 41P/Tuttle-Giacobini-Kresák (Schleicher et al 2019). The CN imaging was the focus of Paper I; below we concentrate on the morphology and behavior of the dust and the remaining gas species.…”

“…On the other hand, we have generally assumed that such features are not seen, in part, because the dust has low ejection velocities and large velocity dispersions, requiring excellent spatial resolution to be identified. We have also frequently seen approximately stationary sunwardfacing features in some comets, e.g., C/2007 N3 Lulin (Bair et al 2018), 41P/Tuttle-Giacobini-Kresák (Bair et al 2018;Schleicher et al 2019), yet such features are absent in Wirtanen. Wirtanen's historically close apparition should have made the identification of any such features far easier than in most comets.…”

“…This is near the high-end for the sizes of jets derived from coma models, but it is not anomalous. Comets C/1995 O1 Hale-Bopp and 67P/Churyumov-Gerasimenko exhibited jets of radii 15-30 • (Vasundhara & Chakraborty 1999;Schleicher 2006), and C/2007 N3 Lulin had jets of 10 • and 20 • (Bair et al 2018), but the most comparable comet previously modeled was C/1996 B2 Hyakutake (Schleicher & Woodney 2003), which had a primary source of ∼56 • radius (and a smaller secondary source of ∼16 • ).…”

“…Modeling OverviewOur Monte Carlo jet model has seen numerous enhancements since its early success in reproducing the dust jets observed in Comet Hyakutake (C/1996 B2;Schleicher & Woodney 2003). Most relevant here, we added the ability to vectorially apply the excess velocity of dissociation of a parent species to an observed daughter gas species, with the most recent example in our study of Comet Lulin (C/2007 N3;Bair et al 2018). Since most aspects of the model are described in detail in these papers, we only briefly summarize other key aspects of the model.…”

Gas Jet Morphology and the Very Rapidly Increasing Rotation Period of Comet 41P/Tuttle–Giacobini–Kresák

“…As expected, light from the nucleus itself could not be separated from that from the inner coma and a nuclear lightcurve could not be measured. Our primary goal was therefore detection and analyses of gas and/or dust jets, similar to what we have done on several other comets, including Hyakutake (C/1996 B2;Schleicher & Woodney 2003), Lulin (C/2007 N3; Bair et al 2018), 103P/Hartley 2 (Knight & Schleicher 2011, and 10P/Tempel 2 (Knight et al 2012). Going into the apparition, we considered it very likely that T-G-K would have one or more distinctive jets since jets require isolated source regions and the comet's relatively low activity level suggested that much of the surface of the nucleus was inert.…”