We present high resolution (0. ′′ 12 × 0. ′′ 079) observations of the ultracompact Hii region G10.6-0.4 in 23 GHz radio continuum and the NH 3 (3,3) line. Our data show that the infall in the molecular material is largely spherical, and does not flatten into a molecular disk at radii as small as 0.03 pc. The spherical infall in the molecular gas matches in location and velocity the infall seen in the ionized gas. We use a non-detection to place a stringent upper limit on the mass of an expanding molecular shell associated with pressure driven expansion of the Hii region. These data support a scenario in which the molecular accretion flow passes through an ionization front and becomes an ionized accretion flow onto one or more main sequence stars, not the classical pressure-driven expansion scenario. In the continuum emission we see evidence for externally ionized clumps of molecular gas, and cavities evacuated by an outflow from the central source.

We have mapped the ultracompact H ii region, G5.89Ϫ0.39, and its molecular surroundings with the Submillimeter Array at angular resolution in 1.3 mm continuum, SiO , and eight other molecular 2Љ .8 # 1Љ .8 J p 5 r 4 lines. We have resolved for the first time the highly energetic molecular outflow in this region. At this resolution, the outflow is definitely bipolar and appears to originate in a 1.3 mm continuum source. The continuum source peaks in the center of the H ii region. The axis of the outflow lines up with a recently discovered O5 V star. Subject headings: H ii regions -ISM: individual (G5.89Ϫ0.39) -ISM: jets and outflows -stars: formation

Submillimeter Array observations of the massive star-forming region IRAS 18089Ϫ1732 in the 1 mm and 850 mm band reveal outflow and disk signatures in different molecular lines. The SiO (5-4) data show a collimated outflow in the northern direction. In contrast, the HCOOCH 3 (20-19) line, which traces high-density gas, is confined to the very center of the region and shows a velocity gradient across the core. The HCOOCH 3 velocity gradient is not exactly perpendicular to the outflow axis but between an assumed disk plane and the outflow axis. We interpret these HCOOCH 3 features as originating from a rotating disk that is influenced by the outflow and infall. On the basis of the (sub)millimeter continuum emission, the mass of the central core is estimated to be around 38 M , . The dynamical mass derived from the HCOOCH 3 data is 22 M , , of about the same order as the core mass. Thus, the mass of the protostar/disk/envelope system is dominated by its disk and envelope. The two frequency continuum data of the core indicate a low dust opacity index in the outer part, decreasing b ∼ 1.2 to on shorter spatial scales. b ∼ 0.5

Correlations between magnetic reconnection and energetic ion flow events have been measured with merging force free spheromaks at the Swarthmore Spheromak Experiment. The reconnection layer is measured with a linear probe array and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The most energetic events occur in the reconnection plane immediately after formation as the spheromaks dynamically merge. The outflow velocity is nearly Alfvénic. As the spheromaks form equilibria and decay, the flow is substantially reduced.

We present observations of the W51 high-mass star-forming region at 86 and 110 GHz made with the Berkeley-Illinois-Maryland Association (BIMA) array. The observations include the H 13 CO + (J ¼ 1 ! 0), SiO(J ¼ 2 ! 1; ¼ 0), SO 2 (8 1;7 ! 8 0;8 ), SO 2 (8 3;5 ! 9 2;8 ), 13 CO(J ¼ 1 ! 0), and C 18 O(J ¼ 1 ! 0) lines. We compare the H 13 CO + (J ¼ 1 ! 0) data to earlier work and find that these data support the hypothesis that infall in the W51 region is taking place in several localized regions, each involving on the order of 100 M of gas. The data do not support the hypothesis that the collapse is global, involving tens of thousands M of gas. We calculate dust masses for two dense cores containing ultra-compact H ii regions and find that these masses are consistent with the localized infall model, being on the order of 100 M . We estimate gas column densities from the observations of CO and SO 2 and find them to be consistent with the other mass estimates, assuming abundances from other hot molecular cores.