Location in the Δν − ΔΠ₁ plane of RGB stars with masses above 1.8 M_⊙. The colors indicate the stellar mass, following the same scale as in Fig. 2. Evolutionary tracks of stellar models with α_ov = 0.1 are displayed with thick lines when electron degeneracy is strong in the core, and thin lines otherwise. Circles correspond to RGB stars studied by V16 and star-shaped symbols indicate stars from Yu et al. (2018) with period spacing measured in this study (see Sect. 5.3). The black dashed line corresponds to the average degenerate sequence obtained from observations. The vertical gray dotted line shows the limit of Δν = 9 μHz, above which we have performed new measurements of ΔΠ₁ in Sect. 5.2.