Density perturbation pattern as predicted by three different disk oscillation models. From left to right are presented a 2D model with α = 0.4 (Model 1), a 2.5D model with α = 0.4 (Model 2), and a 2.5D model with α = 0.8 (Model 3). In these representations, the disk is seen from above and the x- and y-axes express the distance from the center of the star in stellar radii. The color scheme indicates the amplitude of the surface density perturbation (Σ′), normalized by the unperturbed value (Σ). Darker colors indicate over-densities and lighter color sub-densities. The line of sight toward the observer is marked in four directions, sampling the V/R cycle in phase from τ = 0. (i.e., maximum V/R) to τ = 0.75.