Optical observations of the potentially hazardous asteroid (4660) Nereus at opposition 2021

Abstract

On 11 December 2021 at 11 UTC, the near-Earth asteroid (4660) Nereus passed the Earth at a distance of 0.0263 au, reaching about 13th magnitude that made it an excellent target for ground-based observations. We observed the asteroid photometrically from 11 October 2021, when it was visible at V = 17.7 mag, until 16 February 2022 (at V = 18.0 mag), and spectroscopically on 10 December 2021 (V ∼ 13.1 mag).Lightcurve analysis of (4660) Nereus gave a rotational period of 15.184245±0.000015 h with amplitude of 0.796 ± 0.052 mag. Fitting the magnitude-phase curve with the standard HG, HG1G2, HG12 functions yielded the following values: HR = 18.68−0.13+0.07 mag, G = 0.30−0.11+0.05; HR = 18.64−0.84+0.42 mag, G1 = 0.21−0.11+0.05, G2 = 0.46−0.23+0.22; HR = 18.61−0.07+0.13 mag, G12 = 0.18−0.18+0.18. The color indices of the asteroid at phase angle of 72.9° were found to be as follows: (B−V) = 0.688 ± 0.084, (B−R) = 1.046 ± 0.073, (V−R) = 0.358 ± 0.047, (V−I) = 0.718 ± 0.050. Its equivalent diameter was estimated as 0.34−0.10+0.07 km. These values, as well as the computed values of G1 and G2 coefficients, indicate that (4660) Nereus belongs to E-class asteroids. The same conclusion was made based on the spectra obtained.