P_r of comets in the J band (λ_C = 1.25 μm) as a function of phase angle. The data for comets C/1995 O1 (Hale–Bopp), C/1975 V1 (West), and 1P/Halley are from the database of comet polarimetry (DOCP; Kiselev et al. 2010), and the data for comets 209P/LINEAR and C/2013 US10 (Catalina) are from Kuroda et al. (2015) and Kwon et al. (2017), respectively. The red symbols show the results for 252P. The solid curve denotes the interpolated average α dependence of the comets, as a result of Eq. (11). The shaded area (in pink) covers the 3σ region of the average trend. The best fit (minimum χ²) parameters weighted by the square of the errors in J band are b = 38.64 ± 1.74%, c₁ = 0.77 ± 0.31, c₂ = 0.70 ± 0.11, and α₀ = 21.85° ± 2.02°.