Observed (black) and best-fit model (red; with parameters in Table 1) position–velocity diagrams of the C¹⁸ O (upper panels) and H¹³CO⁺ (lower panels) emission along the major (left panels) and minor (right panels) axes of the flattened envelope passing through the protostellar position. Vertical and horizontal dotted lines denote the systemic velocity of 8.34 km s⁻¹ and the protostellar position, respectively. Vertical green dashed lines show the velocity range that was not included in our model fitting, V_LSR of 7.7–8.9 km s⁻¹, because of a possible contamination from the outflow. Contour levels are from 3σ in steps of 5σ, where 1σ is 3.8 mJy beam⁻¹ in the C¹⁸O emission andis 3.3 mJy beam⁻¹ in the H¹³CO⁺ emission.