High spatial resolution observation (~ 5 arcsec) were made for CH3OH, HCOOCH3, and (CH3)2O toward Orion-KL using the Nobeyama Millimeter Array. The spatial distribution of CH3OH appears to be well elongated along the line connecting IRc2 and “the southern condensation (SC)”. The HCOOCH3 and (CH3)2O emissions appear to be well concentrated to SC with an angular size of ~ 6.5 arcsec. We derive the total column densities 6.8 × 1017cm−2, 1.4 × 1016cm−2 and 2.7 × 1016cm−2 for CH3OH, HCOOCH3, and (CH3)2O, respectively, at the core of SC.

The 111−-101+ transition of NH2D and the 21−20 E transition of CH3OD were mapped toward Orion-KL with the Nobeyama Millimeter Array. The synthesized beamwidth is 4″ to 5″. NH2D and CH3OD are mainly distributed over the peak-intensity regions of NH3 and CH3OH in Orion A, respectively. These results suggest that “most” of the gas-phase ammonia and methanol in the region of Orion-KL originate from dust grains.

Interferometric observations of the SiO (J = 2 − 1) line are carried out toward a low-mass-star forming region, Bl, and a massive star forming region, Ori KL. Production mechanisms of SiO in these regions are discussed.

It is known that stars in GMCs are often born as clusters. Recently, near infrared imaging has enabled us to study the young stars within molecular clouds (e.g., Lada & Lada 1991). Orion Molecular Cloud 2 (OMC2) is located 12' north of the Trapezium cluster in the Orion A cloud, and contains a cluster of about 20 near-IR sources and several FIR sources distributed within a diameter of 0.2 pc (Rayner et al... 1989; Johnson et al. 1990; Mezger, Wink, & Zylka 1990). By large scale mapping observations using the NRO 45 m telescope, this infrared cluster is found to be associated with a dense molecular core (Tatematsu et al. 1993, Umemoto et al. 1993). The region was observed using the Nobeyama Millimeter Array (NMA) to elucidate the structure and cluster formation process within a core.

By combining new NRAO 12m data with previously published BIMA data, we have obtained very high signal-to-noise maps of HCO+ in the Orion B core, which contain information on both the large- and small-scale emission and put new constraints on the gas’ physical conditions.

The Orion bright bar is a prominent ionization front located approximately 2’ southeast of the Trapezium stars. Because this ionization front is seen almost edge-on, it provides an opportunity to study the interaction between the HII region and the adjacent molecular cloud. The molecular bar has been thought to be a narrow layer of ~ 50” (0.1 pc) in width parallel to the ionization front with enhanced temperature, density and column density. The molecular gas outside the ionization front was redshifted with respect to the ambient molecular cloud by 1-2 kms−1 (Omodaka et al. 1984, 1986, 1992), suggesting that the expanding HII region generated by the Trapezium stars had driven a shock wave into the molecular cloud at the southeast of the bar. This layer is exposed to intense UV radiation from the Trapezium stars, resulting in the formation of photodissociated regions.

We have made aperture synthesis observations of CS(J=1-0) line and 49 GHz continuum in the Orion bright bar with the Nobeyama Millimeter Array. Figure 1, a map of integrated intensities of CS, clearly revealed fine structures of the molecular bar and more than six prominent features are confirmed. It is noted that these features are lined up at 30” from the ionization front inside the molecular cloud.

We observed W49A with NMA. We found rotational infall motion toward massive core. The rotational velocity and the infall velocity are 2±1 km s−1 /pc and 5±2 km s−1, respectively.

A multi-level, non-LTE, (non-LVG) radiative transfer code has been applied to HCO+ observations of W 49 A north. Profiles of both the J=1-0 and J=3-2 transitions are successfully reproduced with a variety of cloud models.

We present maps of M17 SW cloud core in the CS J=1→0 line and the 49 GHz continuum obtained with the Nobeyama Millimeter Array.

A high-spatial-resolution observation of the NGC 7538 molecular cloud core has been performed with the Nobeyama Millimeter Array. We report on the detailed structure of the region including IRS1-3 complex and IRS11 based on the CS J = 1−0 line observational results.

The observation was done in December, 1988. The field center was at R.A. (1950)=23h11m36.8s, Dec (1950)=61° 11′ 10″ which is between IRS1-3 complex and IRS11. The primary beam, 2.5’(FWHM), was large enough to cover both IRS1-3 complex and IRS11. We used 18 baselines, and the synthesized beam became 10.6″×10.4″ (natural weight).

Millimeter-wave continuum sources in NGC 7538 region were observed with the NRO 45-m telescope and Nobeyama Millimeter Array. NRO 45-m telescope observations showed that the compact region which includes IRS1, IRS2, and IRS3 has a strong millimeter-wave intensity excess, cf. figures 1, and 2.

We present multi-line millimeter interferometer maps HII single dish observations of the G5.89-0.39 ultracompact HII region. Radiative transfer modelling suggests an overall collapse.

With the VLA in the D configuration we have mapped the (J,K) = (1,1) and (2,2) NH3 lines toward a molecular cloud core in NGC 2024. This region, which contains one of the most highly collimated molecular outflows (Richer et al. 1992), has been studied extensively using a variety of techniques, including dust continuum in the far-infrared (FIR) wavelengths (Mezger et al. 1988, 1992), and molecular lines (see Barnes & Crutcher 1992 and references therein). We find that the molecular condensations associated with FIR 5, 6, and 7 (Mezger et al. 1988, 1992) have kinetic temperatures TK ≃ 40 K. We also find a perturbation of the molecular gas near FIR 6 and FIR 7 in terms of broadening of the ammonia lines. These results suggest that these condensations may not be protostars heated by gravitational energy released during collapse, but that they have an internal heating source. A flattened structure of ammonia emission is found extending parallel to the unipolar CO outflow structure, but displaced systematically to the east. The location of the high velocity outflow along the surface of the NH3 structure suggests that a wind is sweeping material from the surface of this elongated cloud core. Figure 1 is an overlay of the VLA ammonia emission (dotted area) on top of the C18O emission (thick contours) and the CO outflow (thin contours).

Monitoring absorption lines in the radio spectra of compact extragalactic sources that lie behind local molecular clouds provides a method for exploring the AU-scale structure of the foreground clouds.

High-resolution mm continuum observations are especially well suited to detect clumpy structures in molecular clouds. In this paper we concentrate on the Mon R2 cloud core which is associated with a cluster of IR sources. Walker et al. (1990) made a 1.3 mm map with 30″ resolution. They found an unresolved and elongated structure extending from NE to SW. Here, we discuss high-resolution continuum maps at 870 and 1300 µm showing a rich clumpy structure on the scale of several 10 arcsec. The clumps are probably intimately linked to the star formation process in Mon R2.

The Taurus dark cloud is one of the nearest active sites of low-mass star formation. The IRAS satellite has discovered numerous low-luminosity far-infrared sources in this cloud, some of which are completely invisible at optical wavelengths. There are several arguments suggesting that the invisible sources are low-mass protostars which are younger than T Tauri stars and powered by the accretion of infalling gas and dust (Adams, Lada, & Shu 1987; Beichman et al. 1986; Myers et al. 1987; Kenyon et al. 1990)

Tamura et al. (1991) made a near-infrared imaging survey of a complete, flux-limited sample of cold IRAS sources in the Taurus dark cloud, of which 8 are optical T Tauri-like objects and 16 are optically invisible sources. They identified all 24 sources with near-infrared counterparts; one is entirely nebulous without a point-like source, and the others generally have an unresolved peak with or without an extended component at 2.2 µm 75 % of the 24 sample sources are associated with infrared/optical nebulosity about 1000 AU to 10000 AU in size. A number of the sources show a clear bipolar or monopolar morphology, suggestive of a close relation of the nebulosity with a bipolar mass outflow; the nebulosity is due to scattering of light from the central source by the dust associated with the mass outflow extending to the poles of a circumstellar dust disk.

SVS 12 is an embedded infrared source which is the probable exciting star for HH 12. The source has a “class I” IRAS spectrum and about 20 L© luminosity. Differential reddening between the star (J-K ≥ 6 mag) and the adjacent infrared reflection nebula (J-K= 3 mag) suggests the presence of dense circumstellar material (Stapelfeldt et al. 1991). SVS 12 was observed with the OVRO interferometer in the 13CO 1-0 and CS 2-1 lines and associated continuum, and at the CSO with a bolometer and in the CS 5-4 and CS 7-6 lines.

We have undertaken 3mm continuum and 13CO line observations of 10 Young Stellar Objects with the Plateau de Bure Interferometer (PdBI) in a snapshot mode. We discuss here mainly the continuum dust emission (opacity index β and source extent).

The Nobeyama Millimeter Array Survey for protoplanetary disks has been made for 19 protostellar IRAS sources in Taurus; 13 were invisible protostars and 6 were youngest T Tauri stars. We observed the 98 GHz continuum and CS(J=2-1) line emissions simultaneously with spatial resolutions of 2.8”- 8.8” (360 AU-1,200 AU). Unresolved continuum emission was detected from 5 of 6 T Tauri stars and 2 of 13 protostar candidates. The continuum emission arose from compact circumstellar disks. Extended CS emission was detected around 2 T Tauri stars and 11 protostar candidates. There is a remarkable tendency for the detectability for the 98 GHz continuum emission to be small for protostar candidates. This tendency is explained if the mass of protoplanetary disks around protostars is not as large as that around T Tauri stars; the disk mass may increase with the increase of central stellar mass by dynamical accretion in the course of evolution from protostars to T Tauri stars.

We report the initial results of a study of the chemical composition of the T Tauri circumstellar disk. The excitation and distribution of CS and HCO+ are discussed. These two molecules behave quite differently in the YSO environment.