Position-velocity map along the orbital direction for the ²⁸SiO v = 0 J = 16−15 line. Negative position offsets are westward. The cross marks the position of the continuum peak (origin of coordinates) and the adopted systemic velocity. The brightness units are Jy beam⁻¹. The contours are logarithmic, with a step of a factor of two and a first level of ±20 mJy beam⁻¹. The dashed contours represent negative values.