Position–velocity diagram of the H¹³CO⁺ emission along the (a) major and (b) minor axes of the flattened envelope passing through the protostellar position. Velocity axes are in units of km s⁻¹ in the LSR frame, and offset axes are in arcsecond with respect to the protostellar position. Vertical and horizontal green lines denote the systemic velocity of 8.34 km s⁻¹ and the protostellar position, respectively. Contour levels are 3σ, 6σ, 10σ, 15σ, and 20σ and then in steps of 10σ, where 1σ is 3.3 mJy beam⁻¹.