We report a large scale mapping observation of the Galactic center region in the CO (J=2-1) line using the Tokyo-NRO 60cm survey telescope. Distribution of the CO (J=2-1) emission in the I-V plane suggests that molecular clouds forms a huge complex (Nuclear Molecular cloud Complex, NMC). Tracers of star formation activities in the last 106-108 years show that star formation has occured in a ring ~ 100 pc in radius. Relative to this Star Forming Ring, the molecular gas is distributed mainly on the positive longitude side. This may indicate that much of the gas in NMC is in transient orbit to fall into the star forming ring or to the nucleus in the near future.

Molecular clouds in the Galactic center region are distributed mainly along the Galactic plane and have filamentary shapes with several clumps (Bally et al. 1987, Tsuboi et al. 1989). The “50-km.s−1 molecular cloud (M-0.02-0.07)”, which is located ~3’ east from Sgr A West, is one of most remarkable clumps on these molecular filaments. The intimate relation between this cloud and Sgr A East has been mentioned by many authers (e.g. Ho et al. 1986). Several compact HII regions are located toward the cloud (Ekers et al. 1983). The recombination line velocities correspond to the molecular line velocities in the cloud (Goss et al. 1987). Thus this cloud is one of active star forming regions near the Galactic center.

We observed the 50-km-s−1 molecular cloud in CS J=1-0 emission line (48.991 GHz) using the Nobeyama Millimeter Array (NMA) to reveal the detailed structure of the star forming regions near the Galactic center.

We have observed Sgr B2 with NMA.Blue- and redshifted features revel the structure of massive core. Massive core was formed by a cloud collision and massive star formation took place by means of collapse of massive core.

We demonstrate that it is possible to understand observed radial velocities of molecular clouds close to the Galactic Center as being due to motion of this material in an accretion disk. Our models indicate a stationary disk with a radial mass flow rate of 10-1.8 Mʘ/yr with a viscosity of 1.9 · 103 pc km/s at 100 pc from the Galactic Center and a radial dependence of it, that goes approximately like the square root of the radius from the Galactic Center.

Several topics in massive star formation are discussed. These include chemical markers of the evolutionary state of massive protostellar cores, kinematic evidence for gravitational collapse, and studies of massive star formation in different environments.

We have made aperture synthesis multifield observations of Orion Molecular Cloud-1 (OMC-1) in the CS (J=1-0) line using the Nobeyama Millimeter Array (NMA), and obtained 9” resolution maps over 10’ length. The OMC-1 ridge shows a wiggled structure. The position angle of whole the ridge is ~ 0° - 10°, but ~ 20° - 30°around the clumps. It is possible to make this structure by the magnetic field with a position angle of ~ 150°. We also found filamentary structures in the northwest of Orion-KL, with a length-width ratio of more than 25, which are made by the gas flow from Orion-KL.

A map of SiO (J = 2 − 1) in Ori KL has been obtained with 2.8” spatial resolution by using Nobeyama Millimeter Array. The distribution of SiO evidences an interaction between outflow and dense gas around IRc4 and IRc5; these infrared sources are thus considered to be shock-heated regions. Since distributions of (CH3)2O and HCOOCH3 have a peak at the IRc5 position, such shock heating seems to play an important role in production of these molecules. Detection of CH3OD around the interacting region most likely suggests that CH3OH is evaporating from dust grains. (CH3)2O and HCOOCH3 may be produced by gas-phase reactions starting from injected CH3OH, or they might be evaporated from dust grains.

Recent molecular line observations of HH flows (HH objects and optical jets) have revealed abundant evidence of interactions between protostellar winds and the surrounding molecular clouds. HCO+ observations taken with the BIMA Array have traced out the distribution of both stationary and high-velocity gas near the protostellar objects HH 7-11, L1551, and HH 34.

We make detailed comparison between the high resolution CO (J=2-l, 1-0) maps obtained with the OVRO Millimeter Array and the 2.12 µm H2(v=1-0) S(1) multi-channel images obtained using a Fabry-Perot system with the UKIRT Infrared Array Camera. Both datasets cover an interstellar shockfront region in the vicinity of the Galactic supernova remnant IC 443, and provide complementary information of the strongly shocked molecular gas on scales of 0.01 pc and a few km s−1. Combining our data with other atomic/molecular line probes, we find that a combination of bow-shock and cloud internal shock can best describe the interface between the supernova blast wave and pre-existing molecular clouds.

A variety of evidence suggests that at least 50% of T Tauri stars are surrounded by disks of gas and dust. Inferred disk properties are compatible with those generally attributed to the solar nebula, before the formation of planets. Millimeter-wave aperture synthesis mapping of molecular line and dust continuum emission from T Tauri stars provides a direct way to ascertain if disks are present. The technique enables detailed studies of disk temperature and density distributions, chemical properties and velocity fields. These results inform our understanding of both star formation and solar system evolution. We review the observations to date and discuss directions for future research.

Observations of circumstellar disks with Nobeyama Millimeter Array (NMA) are presented for the following two topics. The first one is on the continued NMA survey for 13 complete samples of protostar candidates associated with Taurus molecular cloud. The observation confirmed the previous result that protostar candidates do not have detectable 3 mm continuum emission except for the two sources L1551-IRS5 and IRAS 04365+2535. This sets the upper limit to the circumstellar disk mass to be ~0.03 Mʘ for the protostar candidates. The disk mass for protostar candidates tends to be smaller than that around young T Tauri stars, suggesting that it may increase in the course of evolution from protostars into T Tauri stars. The second topic is on the detection of CO (J=1-0) emission toward GG Tau. The observations with the 45-m telescope and with NMA show strong evidence of the CO emission arising from a rotating disk with its size significantly extended with respect to the dust disk. Depletion of CO gas in the GG Tau disk is discussed.

Aperture synthesis CS(J=l-0) observations were made of the expanding clumpy shocked shell that was found around the redshifted CO outflow in NGC 2071 during our previous study (Kitamura et al. 1990). It has been revealed that previously identified clumps in the shell comprise several small subclumps. The decelerating shock and Rayleigh-Taylor instabilities seem to be probable mechanisms by which the subclumps are formed in the shock-compressed shell.

We report the results of CO J=l—+0 mapping of portions of the blue outflow lobe of L1551 with ~ 7” (N-S) × 4” (E-W) resolution, obtained with the 3-element OVRO millimeter array. Comparison of our interferometer mosaic with lower resolution single-dish data shows that we resolve the strongest single-dish emission regions into filamentary structures, such as are characteristic of shock fronts mapped via their near-infrared H2 emission in other outflow sources.

We present the aperture synthesis observations of the CO molecular outflows associated with the low-mass young stellar objects embedded in B335 and Bl. We used the Nobeyama Millimeter Array and obtained the angular resolutions of 8.1” × 5.0” for B335 and 6.5” × 4.4” for B1.

We summarize the evidence for protostellar collapse in B335.

The region containing Haro 4-255 FIR is studied in CS (1-0) with the 45 m telescope and the Nobeyama Millimeter Array. We have detected intense CS outflow. The CS abundance is found to be enhanced in the outflow lobe. The aperture synthesis data show two groups of emission, one of which is likely to impede the blueshifted CS lobe.

We have reported NMA observations of HH83 with CS (J=2-l) line. The interacton between the outflow and the molecluar cloud is found.

The first results of large-area mapping observations of nearby giant molecular clouds in the CO(J=2-1) emission are presented. The CO(J=2-1)/CO(J=1-0) luminosity ratio is 0.75 and 0.62 for the Orion A and B clouds, respectively. These values are consistent with those observed typically in disks of galaxies (−0.6), and are significantly lower than large values (≳1) often observed in active star-forming regions in galaxies. Active star-forming regions in galaxies cannot be explained by ensemble of Orion-like GMCs; they may contain a different population of molecular clouds with high J-2-1/J=1-0 luminosity ratio.

Clumps and filamentary structures have previously been observed in the extended molecular ridge of OMC-1 (see below). The region is affected by multiple outflow components, shock emission that extends 0.5 pc from the BN/KL core, and a foreground HII region expanding into the cloud. The region also displays a complex kinematical character, with a large scale shift in radial velocity along the ridge, multiple cloud velocity components (Womack et al. 1993), and fast gradients across constituent cores (Harris et al. 1983, Wiseman and Ho 1993).

To clarify the structure and kinematics of the region, we have used the VLA to observe with high (0.3 km s−1) velocity resolution and high (8”) angular resolution the NH3 (1,1) and (2,2) rotation-inversion lines over 20 adjacent fields covering a 3’ by 8’ region encompassing the KL region.

We have made aperture synthesis observations of CS(2-1) emission using the Nobeyama Millimeter Array (NMA), and obtained ~ 2” × 3” (0.005 × 0.008 pc) resolution image to investigate the velocity structures of Orion-KL. We found not only well-known expanding doughnut but the expanding hemisphere in the Orion-KL hot core.