Relationship between P_min and α₀ for dark asteroids. Markers indicate the asteroids’ spectral type based on Tholen, SMASSII, or Bus-DeMeo classifications (Tholen 1984; Bus & Binzel 2002; Lazzaro et al. 2004; DeMeo et al. 2009; Hasegawa et al. 2024). The cross markers represent asteroids classified as Ch-types in previous studies (Bus & Binzel 2002; Lazzaro et al. 2004; DeMeo et al. 2009; Hasegawa et al. 2024). Only P_min values fitted with sufficient data points (three or more data points near α_min, i.e., 5 < α < 15) are plotted. The empty circles show the S-type asteroids for the comparison (Gil-Hutton & García-Migani 2017; Lupishko 2019; Bendjoya et al. 2022).