We report on extensive submillimetre wavelength observations in the CO J = 3-2 and 4-3 lines towards a sample of star formation regions. The observations have been obtained using the Queen Mary College Submillimetre Heterodyne Receiver at the UKIRT 3.8 m telescope. The data include observations and maps of NGC 2024, S88, W3, S140, CRL2591, NGC 2264, K3-50, G35.2-0.74, ρ Oph A, M17, W51, S68, S106, NGC 1333, DR21 and W49. Several new bipolar flow sources have been detected in NGC 2024, S88 and NGC 2264. Comparisons between the spectra in the CO J = 1-0, 2-1, 3-2 and 4-3 transitions will be discussed in terms of their excitation, in particular for the gas in the high velocity line wings, where we have attempted to estimate the densities and relative abundances of the flow material.

In a search for very high density (n ≳ 107 cm−3) regions, the Millimeter Wave Observatory 5-m telescope was used to observe several submillimeter lines. The regions studied were Orion A, M17, S140, and NGC2024. The lines were CS(J=7-6), H2CO(JK-1K1=515→414), and HCN(J=4-3). These data are combined with data at millimeter wavelengths to derive the volume density and the results are compared to those deduced from millimeter lines alone (Snell et al. 1984). In NGC2024, higher densities (≳ 107 cm−3) are clearly indicated by the sub-mm lines than were derived by Snell et al. In M17, derived densities are also higher, but uncertainties overlap the Snell et al. solutions. The range of densities derived from CS and HCN are consistent. The sub-millimeter lines of these species appear to be good probes of the highest densities present in regions of active star formation.

Detailed maps of 70 OH and H2O masers associated with star-forming regions have been made with the VLA at an angular resolution of ∼2″ arc. The absolute position accuracy is 0″.5 for both the OH and H2O observations, and the relative position accuracy of maser spots within a group is 0″.1 for each species. For about half of the sources compact H II regions are detected at 22 GHz with 0″.1 positional accuracy relative to the strongest H2O maser. Preliminary results are presented, with emphasis on the spatial relationship between the OH and H2O masers and compact H II regions.

The Orion–KL region has been studied extensively by observations of lines originating from highly–excited rotational levels of CO (see Watson et al. 1985). The lines arise in the shocked gas that lies at the interface of the hypersonic mass outflow of a newly–formed star and the quiescent material in Orion. The CO line intensities are sensitive to the physical conditions in the shocked region, and have been interpreted with a kinetic temperature T ≃ 600 K and density n(H2)≃ 2 × 106 cm−3. Recently, pure rotational lines of OH have been detected as well in the far-infrared spectrum of Orion. Since the OH and CO molecules differ substantially in their energy level structure and in other properties, it is of interest to investigate whether the OH excitation probes the same physical conditions as the CO excitation or whether the two molecules reside in different parts of the shock.

The maser emission of the J = 1-0 lines of SiO in vibrationally excited states has been detected in two regions of massive star formation, W51 IRS2 and Sgr B2 MD5. The SiO masers apparently coincide with strong H2O masers in each source within the uncertainties of < 5″. Their velocity ranges fall within those of the nearest H2O masers (Figure 1). In W51 IRS2 the maser emission is observed only in the v = 2 state, and the upper limit of the v = 1 line (3σ) is 1/15th of the v = 2 line intensity. The v = 1 emission found in Sgr B2 MD5 is five times stronger than the marginally detected v = 2 emission (Figure 2). Their luminosities are comparable to those from the corresponding maser in Orion.

In most places where molecular hydrogen exists in the interstellar medium, it will be found in the ground vibrational and ground electronic state. This will not be so, however, near 0 or early B stars where, in the region just beyond the ionization boundary, populations will be determined by UV fields up to 105 times more intense than the mean interstellar value (4 × 10−16 ergs cm−3 s−1 = 1 Habing unit). The H2 absorbs Lyman-Werner band photons longwards of λ91 nm and subsequent decays to the ground electronic state may lead to dissociation (vibrational continuum) or to one of 14 vibrationally excited states. Molecules in these states have lifetimes of order 1010 s and, in the intense fields, will be exposed to further Lyman-Werner excitation. The probability of dissociation is therefore greatly enhanced by this ‘multiple excitation’, since the number of lines available to vibrationally excited H2 is many times that available to ground-state H2 (Shull, 1978).

Near infrared (2 micron) emission lines from molecular hydrogen provide a powerful probe of the morphology and energetics of outflows associated with stellar birth. The H2 emission regions trace the location of shock waves formed when the high velocity outflow from young stars encounters dense quiescent gas. Since H2 is the dominant coolant of the hot post-shock molecular gas, the H2 lines provide a measure of the fraction of the total mechanical luminosity radiated away from the cloud.

Using an InSb photometer/spectrophotometer attached to the 1-m ESO telescope (La Silla, Chile), we searched for the near-infrared emission from the Sharpless regions S269, S271, S307, and S311. These regions appear on the Palomar Sky Survey red plates, as bright visible nebulae, and have extended radio continuum emission.

NGC 3603, one of the most massive H II regions in our galaxy, shows recent star forming activity (Frogel et al. 1977; Tapia 1981; Persi et al., 1985). In this paper we report new near-infrared maps and photometric observations in the complex region surrounding Irs 9, Irs 2 and Irs 8. Most data were gathered at the 1.5-m telescope of CTIO, using an InSb photometer. Tables 1 and 2 synthesize the observations and the results of the photometry. While the low resolution K map (Figure 1) shows basically the previously reported features, the high resolution K and L maps (shown superimposed in Figure 2), show that Irs 9 is the brightest source in the field, clearly resolved from Irs 2 and Irs 8. The presence of a previously unreported source some 22″N and 5″W of Irs 2, should be further investigated. The spectral distributions derived from our measurements and from previous ones by Persi et al. (1985) strongly suggest that the 10 and 20 μm fluxes reported by Frogel et al. (1977) at the position of Irs 2, probably correspond to Irs 9. Under this assumption, Irs 9 is probably a highly reddened massive star (1 μm to 20 μm luminosity, L∗ = 2.2 × 104 L⊙) while the luminosity of Irs 2 is less than 102 L⊙. We therefore conclude that Irs 9 is a young massive star surrounded by a warm (Tdust ∼ 250 K) dust envelope; Irs 2 seems to be the less obscured part of an associated H II region, as further corroborated by the Brγ emission and the free-free like spectrum and spectral distribution, as reported by Persi et al. (1985) and in this paper.

We have searched for radio continuum emission at 15 GHz from a number of deeply embedded protostar like infrared objects, using the B configuration of the VLA. The aim was to get high resolution (1″) and high sensitivity maps. For 10 objects (NGC 7538-IRS 3, GL 989, GL 4029-IRS 1, GL 437N, GL 2789, NGC 1333-IRS 13, S235B, GL 4029-IRS 2, R Mon and OMC2-IRS 3) we did not detect radio emission, the 3 upper limit being 0.3 – 0.5 mJy. Positive detections were made for W33A, 0MC2-IRS 4, S 235-IRS 1 and NGC 6334V-IRS 4. The cleaned maps for these objects are shown in Figures 1-4.

W75N is a highly obscured region containing far-infrared sources, masers and molecular clouds. New results are presented showing highly reddened point sources near the maser source W75N(OH). One of these sources appears to be illuminating a newly discovered reflection nebula exhibiting large scale fluorescent molecular hydrogen.

We have searched for the near-infrared emission from selected areas of the star forming region NGC 6357. Six fields of 90x90 arcsec2 centered on the far-IR peaks G353.19+0.91, G353.22+0.67, G353.13+0.64, G353.05+0.56, on the 6-cm radio continuum peak G353.035+0.78, and on the water maser source H20353.27+0.64, were scanned through the K(2.2 μm) filter at the 2.1-m telescope of the Observatorio Astronómico Nacional at S. Pedro Mártir, Baja California, México.

GM24 is a small visible nebulosity in the vicinity of a molecular cloud. In this contribution we present the results of continuum (6-cm) and CO line (J = 1 → 0) radio observations, infrared maps, broad-band photometry and low-resolution spectroscopy as well as long-slit Echelle Ha spectroscopy. We found evidence that the GM24 = PP85 nebula is part of a larger region where star formation occurred in the past 104 years; the region is embedded in a typical molecular cloud with a dimension of ∼ 10 pc and mass of ∼104 M⊙. A compact radio H II region seems to be associated with GM24 and with one of the mid-infrared peaks detected. The nebula is most probably the visible part of an embedded H II region that is starting to emerge from the cloud. The other infrared peaks found in its vicinity (∼ 1 pc) are probably associated with less evolved stellar objects. The complex also shows an extended near-infrared flux which we believe to arise in a reflection nebula. From energy arguments, we found that the luminosity required to power the H II region and keep the cloud at the observed large temperature (TK ≅33 K), is ∼105 L⊙ which is consistent with the infrared total flux from the present measurements and those from IRAS of 4x104 L⊙; this corresponds to the flux of ∼3 BO ZAMS stars. The details of the present work have appeared in the Revista Mexicana de Astronomía y Astrofísica, Volume 11, 83, 1985.

In a series of observations (Mizuno et al. 1981; Mizuno 1982; Nakano et al. 1983), we have carried out the surface photometry of small H II regions which were selected from Sharpless catalogue (1959) by the following properties: (1) small angular size (≦ 10 arcmin), (2) round and simple appearance, and (3) a single BO V star as the exciting star. Properties (1) and (2) are for the convenience of image processing, and property (3) is to avoid the contamination of [O III] emission in the V-band so as to get pure continuum intensity.

As the first part of a program to investigate the thermal emission of dust at millimeter wavelengths, we present maps of the continuum emission from radio-bright HII regions. These maps have been made with a filled aperture telescope, the NRAO 12-m telescope at Kitt Peak, with a HPBW of 70 arc seconds at 3.5 mm. We used a switched dual-beam technique and a restoration algorithm developed by Emerson et al. (1979 Astron. Ap. 76, 92). We compare these maps with maps made at centimeter wavelengths.

We have performed high resolution VLA radio observations for several small H II regions, including the cluster emission nebulae S258, S255, S257, and S256. The region (PP56) between S255 and S257 at λ2 cm reveals significant flux structure close to OH, H2O and infrared emitting sources as shown in Figure 1. The flux densities and positions are indicated in Table 1. Observations of the cometary nebula PP59 (S269) also reveal similar characteristics as shown in Figure 2. These regions are considered to be active star-forming clouds. The cometary nebula PP40 was also observed and we note that its physical parameters are very similar to those of a typical planetary nebula.

The compact H II region MONR2 has been studied with the VLA at 6 and 1.3 cm (Massi, Felli, and Simon 1985). With a resolution of 1″ the source is now well resolved. The H II region has a circular shape 27″ in diameter and a non uniform surface brightness distribution. The peak of the emission is concentrated in a small sharp strip along the SE edge.

A large radio continuum loop of diameter was discovered at G16.5+0.7 on the Bonn 2.7 GHz and NRO 10 GHz galactic plane surveys. The loop is associated with the H II region M16, and the diameter is 60 pc at a distance of 2.8 kpc. Figure 1 shows the loop at 2.7 GHz in gray scale. The spectrum is thermal and the total H II mass is estimated at 3×103 M⊙. If the loop is due to a shell of the same diameter, the mean electron density on the shell is about 4 cm−3. The total thermal energy is about 6×1048ergs. The characteristics are summarized in Table 1.

S201 is an optically visible H II region whose ionizing star is hidden to the sight by heavy obscuration. The radio continuum surface brightness distribution observed at 6-cm with the VLA can be described by two distinct components: a) an extended diffuse structure, which closely reproduces the shape of the observable nebulosity, and b) a sharp bright arc feature on the east side of the extended component, unresolved towards the outside at the resolution of ∼ 4″.

The dynamical properties of the ionized envelopes surrounding massive, newly formed stars can be probed by the measurement of radio recombination lines over a wide range of frequencies. In an expanding envelope, the centroids of the radio recombination lines move progressively to lower velocities with increasing value of the principal quantum number, n. This shift is caused by the free-free absorption on the near side of the envelope combined with non-LTE radiative transfer effects.