Dust Properties of Comet C/2020 V2 (ZTF) at beyond 4 au

Introduction: Comets are considered to be important remnants of the early Solar System. According to prevailing theories, a significant number of planetesimals were expelled to the Oort cloud during the era of planetary formation [1]. Gravitational interactions, such as encounters with passing stars, can disturb their orbits, redirecting them toward the inner Solar System or even ejecting them into interstellar space [2]. Consequently, some interstellar objects and Oort cloud comets travel on hyperbolic paths, making a single passage through the planetary region. Since these objects are visible for a limited time, it is essential to gather as much observational data as possible, even when they remain at large heliocentric distances. Advancements in observational technologies have led to the detection of several active comets beyond 20 au, including C/2017 K2 (PANSTARRS), C/2010 U3 (Boattini), C/2014 UN271 (Bernardinelli-Bernstein), and C/1995 O1 Hale-Bopp [3]. In this study, we report on observations of the hyperbolic comet C/2020 V2 (ZTF), conducted using spectroscopic, polarimetric, and photometric techniques. Comet 2020V2 follows a hyperbolic orbit with a perihelion distance of 2.228 au, an eccentricity of 1.001, and an inclination of 131.61°, reaching perihelion on May 8, 2023.

Modelling. Using our photometric and polarimetric observations of this comet, we attempted to model the physical characteristics of its dust environment. We utilized the state-of-art modeling tools such as Fast superposition T-matrix method [4] and Radiative transfer with reciprocal transactions [5], in combination with the dynamical dust model, to characterize dust properties and their evolution in the coma.

Results. Spectroscopy post-monitoring shows no significant gas emissions, allowing a focus on the dust environment. Photometric data from winter-spring 2022 reveal stable apparent magnitude. The average dust production level Afρ is ~3800 cm, consistent with other distant comets. Near-nucleus polarization is higher in absolute value than typically observed for comets inside 2 au at similar phase angles. Dust color varied from red to neutral on 3 and 6 March. BTA data show dust color shifts from neutral to red with cometocentric distance, stabilizing beyond ~19000 km. Morphological analysis using multiple filters indicates a stable dust coma with a persistent ejection and tail, varying slightly daily. Was determined rotation periods and active region locations, through geometric modelling.                                                                

Acknowledgments

OI and AV is supported by the Slovak Academy of Sciences (grant Vega 2/0059/22) and grants for projects under the Mobility Programme DAAD-SAS. The research of IL was supported by the projects of the Ministry of Education and Science of Ukraine No.0124U001304.

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[3] E. Lellouch et al., “Size and albedo of the largest detected Oort-cloud object: Comet C/2014 UN271 (Bernardinelli-Bernstein)”,  A&A, Vol. 659 (2020).

[4] J.  Markkanen and A. Yuffa, “Fast superposition T-matrix solution for clusters with arbitrarily-shaped constituent particles”, JQSRT 189, pp. 181-188 (2017)

[5] Muinonen et al., “Multiple scattering of light in discrete random media using incoherent interactions”, Opt. Lett. 43, pp.683-686 (2018)