FROM BIPOLAR TO QUADRUPOLAR - THE COLLIMATION PROCESSES OF THE CEPHEUS-A OUTFLOW

We present new high-angular (approximately 2'') and -velocity (approxi mately 0.3 km s-1) resolution observations in the (J, K) = (1, 1) and (2, 2) ammonia lines toward Cepheus A using the VLA D-configuration. A s previously reported, the high-density gas is mainly distributed in t hree clumps, Cep A-1, Cep A-2, and Cep A-3. Cep A-1 and Cep A-3 consti tute an interstellar elongated structure (approximately 2.'3 x 0.'4, o r approximately 0.5 x 0.08 pc), with the stellar activity center locat ed at its northwest edge. We find that Cep A-1 and Cep A-3 are located , respectively, between the two main pairs of the blue- and redshifted CO lobes of the quadrupolar molecular outflow. This implies that the interstellar disklike structure cannot collimate the bipolar outflow n ear its origin in the east-west direction. The high-velocity outflow a nd the photons of its powering source seem to be producing significant perturbations of the morphological, kinematical, and temperature stru ctures at the edges of the ammonia condensations. We suggest that the interstellar high-density condensations are diverting and redirecting the molecular outflow at scales of approximately 0.05-0.5 pc, with Cep A-1 and Cep A-3 splitting in two halves, respectively, the blue- and redshifted lobes of an originally bipolar outflow already collimated i n the east-west direction at circumstellar scales. Part of the high-de nsity gas located at the edges of the interstellar ammonia condensatio ns may be in the process of being incorporated into the general high-v elocity molecular outflow by a dragging effect. However, the overall o bserved motions in the interstellar high-density gas could be bound by the observed mass in the region. HW 2 is embedded in a circumstellar (approximately 3.3 x 2.''3, or approximately 2400 x 1700 AU; pa. = 22- degrees) high-density [n(H2) congruent-to 3 x 10(7)(X(NH3)/10(-8))-1 c m-3] clump of approximately 2(X(NH3)/10(-8))-1 M.. The high rotational temperatures [T(R)(22-11) = 40-50 K] and the large velocity dispersio ns in the ammonia emission (sigma congruent-to 3-4 km s-1) found towar d this position lead us to favor this object as the powering source of the high-velocity outflow. The observed motions of the circumstellar molecular gas could reflect the bound motions of the gas (e.g., rotati on or infall) around a central mass of approximately 10-20 M., or alte rnatively the perturbation of the ps by the wind of the central source . This circumstellar clump could be related to the circumstellar disk previously suggested from infrared continuum and maser line observatio ns. We find that gas temperatures as a function of the projected dista nce r with respect to HW 2 can be fitted by T(R)(22-11) is-proportiona l-to r(-alpha), with alpha = 0.3-0.6. These indices are quite similar to those expected if heating of the molecular gas is via collisions wi th hot dust heated by the radiation of the central star(s). The observ ed luminosity in the region is enough to heat the gas up to the observ ed temperatures. This analysis suggests that similar VLA studies of ra dial temperature profiles in other star-forming regions may be very us eful for understanding heating processes and identifying exciting sour ces.