A comprehensive study of comet 67P/Churyumov-Gerasimenko in the 2021/2022 apparition. I. Photometry, spectroscopy, morphology

Abstract

We present observations of comet 67P/Churyumov-Gerasimenko during its 2021/22 apparition, aiming to investigate its dust and gas environment and compare the results with those obtained in 2015/16 using the same telescope. Quasi-simultaneous photometric, spectroscopic, and polarimetric observations were carried out at the 6-m BTA SAO telescope. The comet was observed on 6 October 2021, 31 days before perihelion, with \textit{g}-SDSS and \textit{r}-SDSS filters, and on 6 February 2022, 96 days after perihelion, using narrowband cometary filters: BC ($\lambda4450/62$~\AA), RC ($\lambda6839/96$~\AA), and CN ($\lambda3870/58$~\AA). These were complemented by images from the 2-m Liverpool Telescope (La Palma). On 6 October 2021, a sunward jet and long dust tail were detected. By 6 February 2022, the dust coma morphology had changed noticeably, revealing a bright sunward neckline structure superimposed on the projected dust tail, along with two jets at position angles of 133$^{\circ}$ and 193$^{\circ}$. Spectra showed strong CN emission, with relatively weak C$_2$, C$_3$ and NH$_2$ emissions. The dust production rate $Af\rho$ did not exceed 200~cm (uncorrected for phase angle) in both epochs. An unusual CN coma morphology was observed, with evidence of an additional CN source associated with dust jets. Geometric modeling of the jets' dynamics indicated an active area at latitude $-70^{\circ} \pm 4^{\circ}$ with a jet opening angle of $20^{\circ} \pm 6^{\circ}$ on 6 October 2021, and two active areas at latitudes $-58^{\circ} \pm 5^{\circ}$ and $-53^{\circ} \pm 10^{\circ}$, separated by longitude $150^{\circ} \pm 20^{\circ}$, producing the observed jets on 6 February 2022. The average particle velocity in the jets was about $0.32 \pm 0.04$~km~s$^{-1}$.