Structural analysis of the dust tail of Comet NEOWISE (C/2020 F3)

Abstract

<p>Comet NEOWISE (C/2020 F3) displayed a highly structured dust tail, exhibiting the most prominent dust tail features visible from Earth since Comet McNaught (C/2006 P1) in the Southern Hemisphere and Comet Hale-Bopp (C/1995 O1) in the Northern Hemisphere. Using images taken by the amateur astronomer community, this dust tail is analysed using the Finson-Probstein model. The comet’s position in the sky in amateur images is calculated using an open source algorithm [1], the position and exact time then calculated, and the dust tail is simulated. This modelled dust tail structure is then projected and overlaid onto the comet image to directly compare and identify similarities and discrepancies between the model and the image. Using the novel analysis method of mapping the image to a plot of dust grain beta against ejection time[2], tail structures can be more easily identified, analysed and tracked over time (where beta is the ratio of force due to solar radiation pressure and that due to the sun’s gravity).</p> <p>Dust tail structures such as syndynic bands and striae (near-parallel linear features) have been identified and characterised in terms of dust ejection time and dust beta values. These structures are tracked over time, and compared to the analysis of similar structures seen in C/2006 P1 (McNaught) [2]. There are some clear differences between the two comets, particularly in the alignment and arrangement of their striae, most likely due to different heliospheric conditions during each comet’s perihelion passage.   </p> <p>These results, all based on amateur observations, provide a thorough description of Comet NEOWISE’s dust tail to contribute to the collection of cometary dust tail profiles currently available. This will enable convenient comparison between comets in the future, and will eventually enable population studies on cometary dust tails and their features. Due to the comet’s very high activity, it also exhibited a rarely seen tail of neutral sodium atoms. This sodium tail has also been parameterised in this work, with an estimated ionization lifetime of the sodium atoms of 17 hours ± 2 hours.</p> <p> </p> <p> </p> <p>[1] Lang, Dustin, David W. Hogg, Keir Mierle, Michael Blanton, and Sam Roweis. 2010.”Astrometry.net: Blind Astrometric Calibration of Arbitrary Astronomical Images”. <em>The Astronomical Journal</em> 139 (5): 1782-1800. doi:10.1088/0004-6256/139/5/1782.</p> <p>[2] Price, Oliver, Geraint H. Jones, Jeff Morrill, Mathew Owens, Karl Battams, Huw Morgan, Miloslav Drückmuller, and Sebastian Deiries. 2019. "Fine-Scale Structure In Cometary Dust Tails I: Analysis Of Striae In Comet C/2006 P1 (Mcnaught) Through Temporal Mapping". <em>Icarus</em> 319: 540-557. doi:10.1016/j.icarus.2018.09.013.</p>