In order to investigate gravitational instability induced by supersonic collisions between small, dense clouds and large, diffuse clouds, we perform the numerical hydrodynamic calculation by SPH code. We show that the large cloud is disrupted by the bow shock induced by the small cloud, and the small cloud is compressed. Final fates of the small cloud are divided into two cases. The first case is that the small cloud is ablated by the ram-pressure of the large cloud and is finally destroyed. The second case is that the central part of the small cloud left from the ablation gravitationally collapses. We discuss the condition dividing these two cases. Our condition show that even if the Mach number of collision velocity is very high, the small cloud can collapse.

CO, J=3 →2, J=2 →1 and J = 1 →0 observations of the extended molecular outflow in the high latitude cloud L 1228 are presented. The 12CO, J=3 →2 and J=2 →1 observations reveal a well collimated and extended outflow. The 12CO, J = 1 →0 observations show that the red shifted part of the outflow has blown a large cavity into the parent cloud and has thus dispersed a significant part of the surrounding cloud.

We present statistics of clump properties in the Orion and Cepheus cloud complexes based on ammonia mapping observations. Surroundings of about 50 IRAS sources earlier found to have associated molecular line emission (Wouterloot, Walmsley and Henkel, 1988) were mapped in NH3(1,1) and (2,2) with the Effelsberg 100-m telescope. Our main interest has been in determining the clump sizes and masses on the basis of the ammonia column density distribution, which together with the observed velocity dispersion lead to a rough estimate of the dynamical state. We also have studied the star-clump separations which should give us estimates of the source ages. Special attention has been paid to comparison of our Orion data with the Benson and Myers (1989, hereafter BM89) results in Taurus because the linear resolutions in the two studies are similar.

A simple calculation of the expected spectral signatures of model protostellar accretion flows suggests how the rotation curve of the accretion disk may be deduced from radio frequency molecular line observations. We compare synthetic observations with actual data to derive rotation curves, braking torques, and minimum magnetic field energies required to effect the braking.

OH megamasers having very high luminosities in the spectral line can be effectively used for the probing of the evolutionary properties of the galaxies in the earliest cosmological epochs. The frequency shift of the emission line uniqually determines the redshift z, which tells about the epoch of emission. One of the important cosmological problems is the investigation of the galaxy mass spectrum in the expanding Universe. There is the empirical relation between the OH and far-infrared luminosities of galaxies. Therefore, if in the earliest cosmological epochs, there were galaxies with sufficient powerful infrared excesses and containing molecular material, they can be detected using the observations of their OH maser emission. The interacting and merging galaxies can be considered as the best candidates for such objects.

We are now carrying out the project to investigate how the primodial solar disk is formed and evolves. One of the central problems of this project is to study the angular momentum transfer in the nebula caused by the magnetic braking or the turbulent mixing in the boundary layer between the surface of the disk and its high temperature corona envelope.

By now, it is well established that massive stars form in giant molecular clouds. Numerous studies have shown that star formation, instead of being spread uniformly throughout molecular clouds, occurs in dense condensations located within these clouds. The physical conditions in these condensations are therefore critical input parameters for any theory of star formation.

For GMC's the two prominent properties are typical. They consist of dense molecular gas clumps concentrating to the GMC centre and filling only a few percent of a total volume. And these clumps participate in chaotic motions with velocities vt exceeding as a rule the sound velocity co at the temperature of molecular gas. This phenomenon is considered as a supersonic molecular cloud's turbulence. The compressibility of turbulent matter becomes very important with such velocities. Thus in application to GMC it is necessary to develop the theory of turbulence and fragmentation under transsonic and supersonic random motions. The hydrodynamic flow velocity field can be divided into the potential and vortical components. When transsonic or supersonic motions prevail the potential component is become more important that stimulates the shock wave's stochastic field development. Ohul'chansky (1988, Kinematics and Physics of Celestial Bodies 4,3) has described this process on the base of Burgers' equation treatment. In this paper we apply this approach for conditions of GMCs that permit the supersonic turbulence' spectrum evolution, the large density fluctuations development, and clumps formation to consider.

Very young stars, known as ‘pre-T-Tauri stars’ (PTTS) or ‘young stellar objects’ (YSO), tend to be surrounded by elongated outflow regions involving ‘Herbig-Haro objects’ (HH). Such ‘bipolar flows’ (BF) are reminiscent of the extragalactic radio sources for which a consensus has formed in 1986 that their jets consist of extremely relativistic pair plasma, of typical Lorentz factor 104±1, generated by an ‘active galactic nucleus’ (AGN); [refs 6,7]. Here I collect new circumstantial evidence for the relativistic nature of BFs.

We present a 3-D hydrodynamical and radiative transfer simulation which suggests that the circular “necklace” of massive star formation in W49A may result from fragmentation via a ring instability during the collapse of a rotating cooling molecular cloud.

A new discussion of the evidences for turbulences in molecular clouds, taking into account line broadenning by saturation at large optical depths, shows that the generally accepted power law dependence of turbulent velocity with cloud size must be revised.

CO, HCO+ and NH3 observations have been carried out towards the high latitude cloud L1642 using the 1.2-m GISS, the 11-m NRAO, the 14-m Metsähovi and the 100-m Effelsberg radio telescopes. The velocity field of the CO gas indicates a core-halo structure. The core component has a constant radial velocity, whereas the halo gas is slightly (> 1 km/s) redshifted, as compared to the radial velocity of the core, and shows velocity gradients towards the cloud edges in a similar way as the HI gas associated with L1642. Within the border of the 13CO emission the mass of the cloud is estimated to be some 76M⊙. In contradiction to Magnani et al.(1985), who claimed that L1642 belongs to a population of very young high latitude clouds which are breaking up, this study supports the view that L1642 is in virial equilibrium and significantly older than 106 yr. The virial equilibrium of L1642 enables a distance determination of ˜ 190 pc to the cloud core.

The IRAM 30-m radiotelescope have been used to obtain, with high angular resolution, the spatial distribution and the physical conditions of the quiescent gas in Orion A, and to search for high velocity molecular gas far away from the well known molecular outflow around IRc2. To study the quiescent gas we mapped a region of 200″×300″ around IRc2 in the J=12-11 and J=16-15 lines of HC3N with angular resolutions of 22″ and 17″ respectively. The left panel of Fig. 1 shows the spatial distribution of the high density quiescent gas around IRc2 for different radial velocities. Beside the already known molecular ridge north of IRc2 (see e. g. Bartla et al. 1983), we find four very thin (nearly unresolved) and long filaments, like “fingers”, stretching from IRc2 to the north and west. The deconvolved size of the longest fingers is ≈180″×15″. From a multi-transition analysis of the HC3N emission we derive H2 densities of 1−8 105 cm−3, kinetic temperatures larger than 40 K and masses of ≈10 Mo. Our high sensitivity observations of the J=2-1 line of CO at selected positions (see right panel ib Fig. 1) show widespread molecular gas with high velocities wings over the region where the molecular fingers and the HH objects are observed (see Fig.1). The high velocity emission occurs over a range of ±40 kms−1. This high velocity gas is more extended (up to 150″ from IRc2) than the very compact (40″) and well studied molecular outflow around IRc2 (see e.g. Wilson et al. 1986). The terminal velocities of the CO wings decrease from 100 km s−1 (corresponding to the very fast molecular flow) to the typical terminal velocities of the extended high velocity gas when the distance to IRc2 changes from 40″ to 60″. The origin of the large scale high velocity gas is unknown, but it is very likely the link between the very compact (40″) and fast (±100 km s−1) molecular outflow around IRc2 and the ionized high velocity gas and the HH objects (Martín-Pintado et al. 1990). The mass, momentum and energy of the extended high velocity gas are crudely estimated to be ≈1 Mo, ≈20 Mo km s−1 and ≈2 1045 erg respectively (i.e. a factor of ≈10 smaller than those of the fast molecular outflow). The location, at the edges of the molecular fingers, and the proper motions of the HH objects (see Fig. 1) suggest the stellar wind is interacting with the molecular fingers. If this interpretation is correct, the influence of the molecular outflow in Orion on the surrounding molecular clouds must be revised.

To use a molecule as a diagnostic of a single star forming region, one has to observe it in different transitions. That is especially true for galaxies, where the beam filling factor is small and unknown. From studies of Galactic objects, the CS molecule is a good tracer of dense gas. Toward the IR galaxies NGC 253, IC 342 and M 82, Mauersberger and Henkel (1989) observed the J=2—1, 3—2 and 5—4 transitions of CS at 3, 2 and 1.3 mm wavelength, repectively. They also measured emission of the isotope C34S, which has an abundance ∼ 1/23 that of the main isotope. This study revealed that the H2 densities in the circumnuclear gas exceed 104, and, in the case of NGC 253, 105 cm−3. In all three cases, the distribution of the dense gas traced out by CS follows the CO distribution.

IC342 (Distance 4 Mpc) is one of the most suitable sources for extragalactic molecular line studies. Toward its nucleus, a great number of molecular species have been found (see Henkel and Mauersberger, 1990); it is also one of the few galaxies investigated in molecular multi-level studies (Mauersberger and Henkel, 1989). In particular, CO shows strong emission: A 7″ resolution interferometric map of the central parts of this galaxy in the 12CO(1—0) transition by Lo et al. (1984) reveals that the circumnuclear molecular gas is distributed in a bar (size 15″ × 70″) (330 × 1500 pc) extending from the nucleus towards the spiral arms. An interferometric map of the 1—0 line of CO by Ishizuki et al. (1990) shows that the inner part of the bar forms a molecular ring of diameter 110 pc. This inner ring also emits 2 and 6 cm continuum radiation (Turner and Ho, 1983). The kinetic temperature of the denser molecular gas is > 50 K (Martin and Ho, 1986). The H2 density of the gas component seen in CO (Eckart et al., 1990) and CS (Mauersberger and Henkel, 1989) is ∼ 104 cm−3.

We have been surveying dense molecular cores in Ophiuchus region including ρ Oph, L234, and L43 with the 4m radio telescope at Nagoya University since 1985. We have already mapped ∼18° × 12° area with 2′ or 4′ grid spacing in 13CO (J=1-0) spectra. We have identified ∼50 dense cores (we call ”13CO cores”). Typical mass, density, and size of the 13CO cores are ∼20 M⊙, ∼3 × 103 cm−3, and ∼0.3 pc, respectively (Nozawa et al. 1990). We also surveyed molecular outflows in 12CO (J=1-0) spectra toward 13 IRAS point sources associated with 13CO cores in Ophiuchus. As a result of the survey, we have found 5 molecular outflows in the filamentary dark clouds and 5 regions exhibiting high velocity wings in the ρ Oph main body.

We present 3-D hydrodynamical calculations of collapsing rotating gas clouds, with molecular cooling. We find that cooling significantly inreases the number of fragments.

in recent years there has been much interest in the study of large samples of molecular cloud cores and related infrared sources in an attempt to observe true protostars - objects in transition between a molecular cloud core and a young stellar object (YSO). We present here a survey of 48 possible protostellar objects chosen initially by their IRAS colours and subsequently observed in (1—0) HCO+ emission at Onsala in Feb 1990. Future observations in (3—2)13CO & (3—2)12CO will be made with the JCMT and in (1,1) and (2,2) NH3 emission with the Bonn 100m telescope.

Both the HII Regions and the Molecular Clouds show broadening of their emission lines beyond that expected from thermal motion and this is ascribed to turbulence. Turbulence in molecular clouds generally agrees with a model where the velocity of motion is determined by the Alfv én velocity.

Turbulence in Galactic HII Regions and Giant Extragalactic HII Regions can also be studied by the width of the emission lines. The magnitude of the turbulent velocities in these regions are characteristically about 10 km/s. There is a general increase in turbulent velocity with the size of the HII Region, and this relation is close to but different from the one third power dependence expected from the most naive application of Kolmogorov theory. When a detailed study is conducted of each Galactic HII Region by means of the structure function, one finds that there is not agreement with Kolmogorov theory.

The Size-Turbulent versus Velocity relation for Galactic HII Regions differs slightly from the better defined velocity relation for Giant Extragalactic HII Regions. This difference is probably due to the fact that the larger extragalactic objects are probably complexes of multiple individual HII Regions. There is no evidence that broadening of extragalactic HII Regions is due to motion about a common center of mass.

We have obtained a high resolution map of the 12CO J=3—2 emission in the vicinity of HH102 in the L1551 molecular outflow. The data reveal the presence of several bright clumps within the thin shell of low-velocity blue-shifted outflowing gas. There is evidence for further fragmentation in the clumps, as signified by the high derived excitation temperatures and low beam-filling factors. The region of peculiarly energetic activity associated with HH102 coincides with the projected location of impact of a radio jet from IRS5 with the dense ambient gas surrounding the outflow cavity.