Morphological Structures in the inner coma of comet C/2020 F3 (NEOWISE)
ATel #13884; Federico Manzini (Stazione Astr. di Sozzago), Paolo Ochner (Uni-PD), Virginio Oldani (Staz. Astr. di Sozzago), Luigi R. Bedin (OAPD-INAF)
on 21 Jul 2020; 14:32 UT
Distributed as an Instant Email Notice Comets
Credential Certification: Luigi R. Bedin BEDIN (luigi.bedin@inaf.it)
We took series of CCD images of comet C/2020 F3 in B, V, R and Ir, with a resolution of 210 to 195 km/pixel, over three consecutive nights from July 18 to July 20, 2020, with the 0.4m Cassegrain telescope at the Stazione Astronomica di Sozzago (Italy - MPC A12). The images show a prominent morphological structure in the inner coma, attributable to the presence of at least one large active area on the cometary nucleus. This structure appears clearly affected by the Solar radiation pressure, still significant at a distance of only 0.53 AU from the Sun. The peri-nuclear condensation looks slightly elongated, and the elongation axis seems to rotate over time. Following an image processing to enhance the weakest details, some semi-circular structures in the solar direction were highlighted, almost concentric to the comet's optocenter. In particular, the stackings of each series of B, V, R and Ir images show a shell fragment with an average distance from the nucleus between 40,000 km and 65,000 km depending on the position angle where it is measured. This shell shows an obvious expansion in the three series of images, with an average expansion speed (measured in three different points of the shell in the solar direction, in PA 135d, 180d and 235d) of 0.494+/-0.050 km/s on the plane of the sky; this is in good agreement with previous measurements made on other comets. These findings may suggest a strong activity in the nucleus, modulated by a rotation with a spin axis geometrically directed nearly towards the Earth during this period. Figures and extra material at https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/ATel/C2020F3/ Federico Manzini (1), Paolo Ochner (2), Virginio Oldani (1), Luigi R. Bedin (3) ((1) Stazione Astronomica di Sozzago, Cascina Guascona, I-28060 Sozzago (Novara), Italy; (2) Department of Physics and Astronomy-University of Padova, Via F. Marzolo 8, I-35131 Padova, Italy; (3) INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova, Italy)
