Observations of an expanding molecular ring in S106

We have mapped the 3 mm rotational transition of HCO⁺ toward S106 with the Berkeley-Illinois-Maryland Array and the NRAO 12 m telescope. The maps show evidence for an expanding molecular ring around IRS 4, the exciting star in S106. The radius of the ring is about 2 × 10¹⁷ cm, and its mass is ≤ 10 M_⊙. The ring is expanding with a velocity of about 2 km s^-1. The ring cannot be supported by rotation; magnetic fields and gas pressure may be important in determining the kinematics of the region. We also observe clumps of high-velocity material which may have been ablated from the ring and entrained in the ionized bipolar outflow.