Fitted positions of the ²⁸SiO v = 1 emission. The crosses are color coded by velocity. We see that there is a clear velocity gradient along the northwest-southeast direction, with blue-shifted emission in the eastern part and red-shifted emission in the western part. This is in good agreement with the result obtained by Matthews et al. (2010) from VLBA data for the v = 1 J = 1–0 transition. The size of the image is about 160 AU  ×  160 AU.