Photometry and polarimetry of comet 46P/Wirtanen in the 2018 apparition

Abstract

Abstract Extensive photometric and polarimetric observations of comet 46P/Wirtanen within the framework of the international 4*P Coma Morphology Campaign were conducted from August 16, 2018 to February 13, 2019 using five telescopes. Digital processing applied to the direct images of the comet revealed the coma and tail, which varied in shape and size. The jet at the position angle 133.5° was found in the images obtained on December 7 and 9, 2018 in the V and R filters. From modelling the formation of the jet, we calculated the coordinates of the north pole of the nucleus rotation axis, α = 220° ± 10°, δ = –20° ± 8°, and the cometocentric latitude of the active area on the nucleus L = 20° ± 6°. The velocity of matter outflow from this active area was estimated to be 0.5 ± 0.05km/ s. The dust production Afρ changed from 12 to 88cm. During our observation period, the coma colour varied from 0.76m to 0.87m and from 0.38m to 0.50m and the reflectivity gradient from 11 to 16.2 per cent per 1000Å and 5.8 to 15.4 per cent per 1000Å for the B–V and V–R spectral bands, respectively. The comparison of the dust production rate of comet 46P/Wirtanen until 2018 and our data for 2018 apparition confirmed its great decrease. The degree of polarization of comet 46P was measured at the phase angles from 27° to 37°. In order to reliably retrieve the polarimetric class of comet 46P, observations at large phase angles are required.