H II regions around OB associations have a thick-shell structure (see, e.g., the Carina and Rosette nebulae), and yet the standard “Hot Interstellar Bubble” model (e.g., Weaver et al. 1977) predicts thin H II shells around a large X-ray emitting volume, when associated with stellar winds. Observations suggest that strong dissipation must occur at the edge of the wind cavity: (i) expansion velocities there are much smaller than predicted by the standard model (e.g., Chu, 1983); (ii) in bubbles around WR stars, overabundances of N, He, etc., are seen, hence the need to cool these WR-produced elements down to observable temperatures (Kwitter, 1981). Also, two theoretical developments are important: (i) new stellar evolution models for massive stars, including mass loss and overshooting in convective cores (e.g., Doom, 1985); (ii) a non-linear theory for heat conduction with steep temperature gradients (Luciani et al. 1985).

The genetic nature of the OB and T-Tau stars connection with stellar associations is at present beyond any doubt. They present the characteristic population of the latter. From this important observational fact follows that all young objects connected with OB and T-Tau stars also originated in stellar associations, and hence, are genetically connected with them.

Stellar winds, bipolar outflows, and supernovae generate strong shocks in molecular clouds. If the molecular gas is magnetized and weakly ionized, shocks slower than about 40-50 kms−1 (C-shocks) emit primarily in the infrared. Faster shocks, or shocks in a weakly magnetized or more highly ionized medium (J–shocks), emit primarily in the ultraviolet and are thus harder to detect in dusty regions. J–shocks in molecular gas are usually dissociative, so that molecular emission lines from such shocks are produced by molecules formed behind the shock front. Observations of fast shocks in molecular clouds can provide valuable insights into energetic events occurring within them.

Atomic hydrogen regions have been observed in λ21-cm emission around a number of galactic HII regions in various stages of evolution (Roger & Pedlar, 1981; Dewdney & Roger, 1982; Roger & Irwin, 1982). These HI zones are almost certainly formed by the dissociation of H2 with Lyman-Werner band photons in the UV from the exciting stars. We describe some results of the computer modelling of the advancement of dissociation fronts with time as functions of various parameters, principally stellar type and ambient gas density. The modelling has shown that for most conditions a substantial HI zone is formed fairly rapidly around a new star. When the dissociation front moves out to a distance where absorbing molecules are predominantly in the ground vibrational state, further advancement of the front is much slower.

The study of the stellar content of nearby OB associations is important for understanding the Initial Mass Function, the study of differential age effects and for a better knowledge of the ambient radiation field, which plays an important role in the interpretation of measurements of gas and dust. Unfortunately, even for the nearest OB associations membership is known very poorly. In most cases no main sequence members of spectral type later than B5 are known. Membership determination using colour-magnitude diagrams suffers from the large intrinsic distance spread. The large angular extent on the sky of most associations makes proper motion measurements difficult to compare because of problems connecting photographic plates with different plate centers. In order to remedy this situation a consortium called SPECTER has been formed at Leiden Observatory. It has been granted observing time on the HIPPARCOS satellite for measuring proper motions of about 10000 candidate members of the OB associations within 600 pc of the Sun. Candidates were selected according to spectral type (not later than F8) apparent magnitude, and location. In anticipation of the HIPPARCOS results, SPECTER will gather a variety of other data. We have nearly completed a program aimed at obtaining VBLUW-photometry (Lub and Pel 1977) of all candidate stars visible from the Southern Hemisphere. Here we discuss the preliminary results for the association Sco OB2.

Extensive molecular line observations have been made of a small region of the supernova remnant IC443 that is strongly interacting with, and shocking a nearby molecular cloud. The observations obtained at the Nobeyama 45-m, Kitt Peak 12-m, and UKIRT 3.8-m telescopes include detailed maps at 15 and 30 arc second resolution in the CO (J = 1-0) and 2-1 lines, and spectra in the CO (J = 3-2) transition. The shocked gas is characterized by a low density and a high temperature. The spatial distribution of the CO shows a remarkable correspondence to maps of shocked molecular hydrogen, and contains a very complex velocity structure, indicating extensive fragmentation. The masses of the clumps are 0.1-0.3 solar masses, and as a system are dynamically unstable. In addition we report a comprehensive molecular line survey towards two of the fragments in IC443, one characterized by the presence of high velocity, and the other by low velocity gas. These results are discussed in relation to the properties of shock-excited gas and theoretical shock-chemistry models. Several other regions in IC443, which appear as strong far-Ir emitters on IRAS images of the remnant, were searched, and also found to be strong emitters of characteristic shocked-gas profiles.

We have searched for associations between supernova remnants (SNR) and IRAS sources. For this purpose we used 117 SNRs from the catalogue of van den Bergh and searched the IRAS Point Source Catalogue for sources associated with SNRs and having a flux density spectrum increasing with wavelength beyond 25 m. For each SNR a square box of area 2 deg2 was searched for sources. The difference between the observed number within the SNR (with 10% radial extension) and the number expected on the basis of source density in the box excluding the SNR itself, was termed the excess. The results are shown in Table 1. There are a few SNRs which show significant excess on an individual basis. The cumulative excess of the rest has a 4 significance. For 58 SNRs with well defined maps, the data in Table 1 show that the significance of excess increases in the shell area. Figure 1 shows the excess as a function of distance to SNR. Also plotted are average excesses for different distance intervals. The increase in excess as distance decreases, strengthens the hypothesis of association with SNR, since at shorter distances, more IRAS sources will be above the threshold of detection.

Cep A is a condensation in the larger CO cloud originally mapped by Sargent (1977, 1979), and contains radio H II regions, OH and H2O masers, a far infrared luminosity of 2.5x104 L⊙, anisotropic mass outflow as seen originally in CO but later in other molecular lines, and a Herbig-Haro object.

At galactic longitudes between 132 and 139 degrees and distances of 2 to 2.5 kpc, the galactic disk contains an unusual concentration of gas clouds, young clusters and OB associations (W3, W4 and W5). The small nebula S 201 is situated to the east of W5, which contains the young open cluster IC 1848. Probably associated with S 201 is one of the originally proposed Bok globules; the region also contains three infrared sources.

A wealth of data is now available on the energetic mass outflows that are associated with young stellar objects. This phenomenon is thought to occur at a very early stage in the evolution of stars of almost all masses. The discovery of this energetic event was first made through observations of the rapidly expanding molecular gas that surrounds many of these young stellar objects. A review of the physical properties, including the energetics and morphology, of the expanding molecular gas is presented in this paper. In addition, the role these energetic winds play in affecting the dynamics of the parental molecular clouds is also discussed. Finally, the results of detailed studies of the structure and kinematics of the high velocity molecular gas are reviewed and the evidence for existance of wind-swept cavities and molecular shells within the clouds are presented.

We review the observational evidence for interstellar and circumstellar size gaseous structures that appear to be collimating the bipolar outflows observed in regions of star formation. In particular, there is growing evidence for circumstellar disk-like objects that may be related to a protoplanetary cloud like the one that once surrounded the Sun. There are similarities between these disks around young stars and that found around the main sequence star β Pictoris. Both flattened structures around L1551 IRS5 and β Pictoris appear to have an inner “hole” with radius of a few tens of AU. On the other hand, there is observational support for focusing and collimation processes acting on the same source from tens of AU (circumstellar dimensions) to tenths of pc (interstellar dimensions).

The fundamental properties of optical and molecular outflows associated with young stellar objects are reviewed. Particular emphasis is placed on a discussion of new results concerning outflow energetics, collimating structures and the relationship between outflow properties and the magnetic field geometry characterizing their host molecular clouds. IRAS observations of YSO mass outflows reveal extended far-IR emission associated with high velocity molecular gas; in the case of L1551 IRS5, the luminosity of the extended emission is ∼10 times the mechanical luminosity inferred from observation of the molecular flow (and thus ≳0.1 the bolometric luminosity of the YSO driving the outflow). Circumstellar disks of size ∼100 au appear to be a common, if not certain outcome of the stellar birth process for stars of ∼1M⊙. In a few cases, it has been possible to resolve disk-like structures associated with YSO outflow sources. In such cases, the disk axes appear to lie along the direction of molecular outflows or stellar jets. The mass outflows (and by inference, the axes of circumstellar disks) show a remarkable tendency to align along the direction of the magnetic fields which thread their host molecular clouds. This suggests that the cloud magnetic field must play an important role in determining the flattening (and perhaps the rotation) of protostellar structures.

Detailed structures in the central parts of several star forming regions have been observed with the Nobeyama 45-m telescope. The disk and flow systems observed in L1551, R Mon, GL490 and S106 regions show the following common characteristics: (1) Double-peaked appearance with a thin central part around the IR source, (2) Cavities exist on both polar sides of the disk, and the low velocity molecular flow fits the shape of the cavity wall and the pattern of the reflection nebula. (3) The flow seems to be accelerated gradually along the wall of the cavity. An empirical model based on these results is discussed.

Observations of the structure and the velocity field in the L1551 bipolar flow were made with the 45m telescope at Nobeyama in the 115GHz 12CO J = 1 – 0 line with high spatial resolution. It was found that the bipolar flow lobes have a clear hollow cylindrical structure and show evidence of a helical velocity field. They appear to rotate in the same direction as the CS disk found by Kaifu et al. (1984). The velocity of the flow in the bipolar directions increases with distance up to ∼ 3′ from the central object, IRS 5. These characteristics coincide with those predicted by the magnetodynamic theory proposed by Uchida and Shibata and indicate the essential importance of the magnetic field in producing such flows and also in the star-formation process itself through the enhancement of angular-momentum loss.

The formation of planets is investigated both in a gaseous nebula and after the nebula has been blown away. The capture of planetesimals by a protoplanet is investigated by taking into account the growth of planetesimals. The time of planet formation is determined as a function of distance from the central star. The formation time of Neptune is found to be 3.9 × 109 yr, value shorter than the age of the solar system. The region where planets form within the stellar lifetime is determined, and it is found that only stars of mass less than several solar masses can have planets. The dust clouds around α Lyrae and β Pictoris are far outside the planet-forming regions. A model for the circumstellar dust cloud is proposed which can explain the basic properties of the β Pic disk.

High velocity OH was detected in absorption in several star forming regions. The supersonic OH shows similar bipolar geometry as the CO. The absorbing OH appears to trace the part of the outflows with the highest velocities and lower densities, and provides information on the structure of the outflows at large distances from the central source. At scales of 0.1 to 0.5 parsecs the outflows are elongated in the direction of the steepest density gradient in the ambient cloud. The transitions in the supersonic OH are markedly subthermal (Tex < 3.8 K), since the radiation that is being absorbed is the cosmic background plus a small galactic contribution. We propose a cooling mechanism for the OH analogous to the adiabatic magnetic cooling of paramagnetic salts used in low temperature physics. Magnetic cooling is a potentially important mechanism for astrophysics.

Previously, mapping of the spatial distribution and velocity structure of vibrational molecular hydrogen (H2) line emission has necessarily been restricted to the central outflow region of the Orion Molecular Cloud (e.g. Beckwidth et al. 1983) where the line intensities are an order of magnitude larger than any other presently known H2 emission source. However, an improved understanding of the role played by highly energetic gas flows in sustaining the observed H2 line emission relies heavily on the collection of comparable data on other active star-forming regions. With this view in mind, we have undertaken a detailed H2 line emission survey of the DR21/W75S molecular cloud complex. We considered this region to be one of the best candidates because it was already known to possess a luminosity (Harvey et al. 1977), CO wind velocities (Dickel et al. 1978, Fischer et al. 1985) and extended H2 emission (Fischer et al. 1981) similar to those seen in Orion.

We have used the 45-m telescope for mapping two CO broad wing sources NGC 2071 and GL490 with a 15″ beam in the J = 1-0 line. We obtained 250 CO and 130 13CO spectra for NGC 2071 and 150 CO spectra for GL490. The observations were made with the highest angular resolution for the CO line and, as well, cover the whole extent of the outflows. The results reveal significant details of the angular distribution of the CO wings.

Observations of star formation sites in a number of molecular clouds, including NGC 7538, NGC 2071, Cepheus A and K3-50A, have been made using the Owens Valley millimeter wave interferometer. The measurements of 12CO, 13CO, CS and continuum emission are at resolutions of order 7″. Continuum emission at 2.7 mm is detected from all the cloud cores and, in general, the 12CO interferometer maps reveal the presence of high velocity, bipolar outflows within 10″ of these continuum sources. Thus, the origins of the outflows are readily identifiable; the flows themselves appear to remain collimated on scales of less than 1017 cm. The orientations of the flows are similar to those seen at lower resolution, except in Cepheus A, where the interferometer is capable of distinguishing between two outflows which are confused in single telescope maps.

It is shown that near infrared polarization is to be expected in star-forming regions and new observations with the UK Infrared Telescope (UKIRT) are reported which include the discovery of a molecular hydrogen reflection nebula in Orion and an extensive dust cloud around S106.