Observations of an expanding molecular ring in S106

The 3 mm rotational transition of HCO(+) toward S106 has been mapped 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 x 10 to the 17th cm, and its mass is 10 solar masses or less. The ring is expanding with a velocity of about 2 km/s. The ring cannot be supported by rotation; magnetic fields and gas pressure may be important in determining the kinematics of the region. Clumps of high-velocity material are observed which may have been ablated from the ring and entrained in the ionized bipolar outflow.