Linear Keplerian model. Red, magenta, and green error bars give major-axis-projected positions and VLsR for the high-velocity peaks (the velocity cuts are indicated by horizontal dotted lines) of the CH₃CN and CH₃OH molecular data (see the legend). Dashed black lines indicate the position of the central source and its VLsR. The blue curves represent a Keplerian fit for the central mass of 15 M_⊙.