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Session 21 - Massive Star Formation & Ultracompact HII Regions.
Oral session, Monday, January 13
We present VLA continuum (2 and 3.6 cm) and line observations (HI 21-cm, C92\alpha and H92\alpha) toward the cometary-like HII region GGD 12-15. The H92\alpha recombination line observations show that the ionized gas has a velocity of 13.8 km s^-1 at the head of the cometary region and reaches a velocity of about 19 km s^-1 at the tail. The C92\alpha emission has a line center velocity of 12.2 km s^-1, close to the velocity of the ionized gas at the head structure, and a narrow linewidth of 2.7 km s^-1. An envelope is detected in the 21-cm HI line in absorption and emission toward the HII region, at 12.2 and 14.7 km s^-1 respectively. Both CII and HI emissions are interpreted as arising from a photodissociated region adjacent to the head of the cometary HII region. The observed kinematics suggest that the HII region is undergoing a champagne flow, with the ionized gas streaming away from the neutral gas toward lower density regions.
Program listing for Monday