¹³CO position velocity diagrams along the direction perpendicular to the outflow: TMC1A (top left), TMC1 (top right), TMR1 (bottom left), and L1536 (bottom right). The color contours start from 3σ and increase by 1σ while the black line contours are drawn at 5σ, 8σ, 11σ, and so on up to the peak intensity. The black solid curves show the best-fit Keplerian curves, while the dashed lines indicate the r^-1 curves. For TMC1A and TMC1 (top row), the blue solid line presents a 0.4  M_⊙ Keplerian curve.