A CIRCUMSTELLAR MOLECULAR GAS STRUCTURE ASSOCIATED WITH THE MASSIVE YOUNG STAR CEPHEUS-A-HW-2

We report the detection via VLA-D observations of ammonia of a circumstellar high-density molecular gas structure toward the massive young star related to the object Cepheus A-HW 2, a firm candidate for the powering source of the high-velocity molecular outflow in the region. This structure has a deconvolved angular size of 3.3'' x 2.3'' (p.a. = 22-degrees), or 2400 x 1700 AU at a distance of 725 pc. For this circumstellar molecular gas structure we derive an average column density N(H2) congruent-to 1 X 10(24)(X(NH3)/10(-8)) cm-2 , a volume density n(H-2) congruent-to 3 X 10(7)(X(NH3)/10(-8)) cm-3, and a mass M(H-2) congruent-to 2(X(NH3)/10(-8)) M.. The ammonia emission shows velocity variations of approximately 4 km s-1 across the condensation. HW 2 was previously reported to be a double radio source, separated by approximately 0.2'' (or 150 AU) with p.a. congruent-to 30-degrees-40-degrees. We suggest that the circumstellar molecular gas structure could be related to the circumstellar disk previously suggested from infrared, H2O, and OH maser observations. We consider as a plausible scenario that the double radio continuum source of HW 2 could represent the ionized inner part of the circumstellar disk, in the same way as proposed to explain the double radio source in L1551. The observed motions in the circumstellar molecular gas can be produced by bound motions (e.g., infall or rotation) around a central mass of approximately 10-20 M. (BO.5 V star or earlier).