VLA AND BIMA OBSERVATIONS TOWARD THE EXCITING SOURCE OF THE MASSIVE HH 80-81 OUTFLOW

摘要

We present high angular resolution Very Large Array (VLA) and Berkeley-Illinois-Maryland Association (BIMA) observations of NH_3, HCO~+, HCN, and SO molecular emission and 1.4, 3.5, and 7 mm continuum emission toward the exciting source of the HH 80-81 system. This object is one of the few massive protostars known to be driving a collimated outflow. We report the first detection of SO 5_5-4_4 molecular emission toward the exciting source of HH 80-81, suggesting that this transition may be a good tracer of molecular gas near massive protostars. We also detected toward this source dust continuum emission at 1.4 and 3.5 mm. From the SO molecular emission and the dust emission we roughly estimated that the molecular mass associated with the circumstellar surroundings of the exciting source of the thermal jet is in the range 1-3 solar mass. Weak and broad (2, 2) ammonia emission was also found in the direction of the jet, suggesting the presence of small amounts of molecular gas at high temperatures (>50 K). The VLA observations show the presence of three ammonia components toward the HH 80-81 region. The brightest component peaks at ～8″ northeast of the thermal jet and is associated with the H_2O maser spots in the region. A second ammonia clump is located about 25″ northeast of the jet and is associated with Class Ⅰ methanol masers. The third ammonia component is located 1′ south of the thermal jet and may be a molecular core, yet without stellar formation. The BIMA observations show that the strongest emission in the HCO~+ and HCN lines originates close to the H_2O maser and covers the same spatial region and velocity range as the brightest ammonia component.