Long-term monitoring of a dynamically new comet C/2020 V2 (ZTF)

Abstract

Comet C/2020 V2 (ZTF) is categorized as a dynamically new long-period comet, making its first approach to the inner Solar system. We have observed this comet for around 32 months (from January 2022 to July 2024) at heliocentric distances from 5.41 au (pre-perihelion) to 5.26 au (post-perihelion) through various telescopes, employing photometric (60 epochs) and spectroscopic techniques (5 epochs). Using these observations, we derived the production rates of different molecules such as CN$(0-0)$, C$_2(Δν=0)$, and C$_3$ and calculated the production rate ratios. The values of the ratios closest to the perihelion are found to be $\log$ (C$_2/$CN) $ = -0.04 \pm 0.03$ and $\log$ (C$_3/$CN) $ = -0.70 \pm 0.04$, which implies a typical carbon composition. The mean photometric broadband colours are found to be $B-V = 0.77\pm0.04$, $V-R = 0.43\pm0.04$, $R-I = 0.42\pm0.06$, and $B-R = 1.19\pm0.04$. The stability of the molecular production rate ratios and mean photometric broadband colours, pre- and post-perihelion, implies a homogeneous composition. The mean reflectivity gradient for $B-V$ colour is $10.90 \pm 3.62$ $\%/1000$ Å; $V-R$ colour is $6.15 \pm 3.51$ $\%/1000$ Å; and for $R-I$ colour is $4.94 \pm 3.56$ $\%/1000$ Å which is similar to the mean value of the dynamically new comets. Additionally, using an asymmetric non-gravitational force model, we report the comet's nuclear radius to be $1.1 \pm 0.1$ km. Our results are expected to provide inputs to the selection of a potential dynamically new comet as a target for the Comet Interceptor mission.

Figures (19)

• Figure 1: Slits corresponding to HFOSC (white) and LISA (grey) are marked on the comet V2 image observed using HFOSC instrument. The dust-tail orientation and the Sun's direction are marked in blue and yellow.
• Figure 2: Spectra of comet V2 (ZTF) observed from HFOSC/HCT (in blue) and LISA/PRL (in black). Prominent emission bands are marked, and the skylines are masked. The spectrum is normalised and spaced by 0.5 relative flux units for clarity.
• Figure 3: Light curve of comet V2 in B (in blue), V (in green), R (in red), and I (in black) filters from the HCT and TRAPPIST. The availability of the comet for observations from the HCT and TN is shown as purple dots (labelled North). Similarly, orange dots are used for the TS (labelled South). They are marked as per the expected magnitude given by NASA JPL HORIZONS. The vertical dotted line, marked in this figure (and all others), represents the perihelion distance, which is 2.23 au. The dash-dot line represents the variation of the phase angle (Sun-Comet-Earth angle) with heliocentric distance.
• Figure 4: Variation of C$_2$/CN with the heliocentric distance. We have marked the 1-$\sigma$ range of the typical region with blue and the 1-$\sigma$ range of the depleted region with orange. The observation from TRAPPIST is marked as blue square, the observation from HFOSC/HCT is marked as red star, and the observation from LISA/PRL is marked as black triangle.
• Figure 5: Variation of C$_3$/CN with the heliocentric distance. We have marked the 1-$\sigma$ range of the typical region with blue and the 1-$\sigma$ range of the depleted region with orange.