Position-velocity diagrams for the nine CH₃CN(37_k−36_k) transitions toward source #1 along the axis marked in the top middle panel of Fig. 8. The vertical line shows the approximate velocity of rest and the two solid curves present a Keplerian rotation curve for a 10(4.5) M_⊙ star at a distance of 2.2(1) kpc. The dashed curves correspond to masses of 5(2.3) and 20(9) M_⊙ (inner and outer curves, respectively) at 2.2(1) kpc.