MASS-LOADED FLOWS .6. A TALE OF THE GALACTIC-CENTER

It has been proposed that the cometary head-tail system of the red sup ergiant IRS7 near the Galactic Centre is produced by the interaction o f a hypersonic galactocentric wind with the stellar envelope. If, howe ver, the envelope is impermeable to the wind and mass is ablated from its boundary surface, such an interaction produces a 'stubby' tail, an d the observed long one cannot be dynamically related to the cometary head. We propose that the wind interacts with a clumpy permeable envel ope and is decelerated primarily in bowshocks around clumps. Thus the ram pressure of the Galactic Centre wind plays no role in determining the head size. The mass-loaded wind cools efficiently by radiation, an d the flow is momentum- rather than energy-driven. As a result, the ta il does not expand much sideways, and has lateral dimensions determine d effectively by the scalesize of the mass-loading region, which in tu rn marks the cometary head.