S106 is an optical bipolar nebula which is elongated in the north-south direction. In the center, there is an infrared source and an ultra-compact H II region, indicating that a young, massive star has been just formed. A high resolution VLA map by Bally et al. (1983) and Felli et al. (1984) revealed a well confined bipolar-shaped H II region with a dust layer in its center. The dust layer which is inclined 25° from the east-west direction is extremely interesting because it seems to indicate that the cold molecular disk is very thin in the central part. A massive molecular core elongated in the east-west direction was observed with CO emission by Bally and Scoville (1982). In the central part, Bieging (1984) reported the detection of a rotating compact disk with HCN emission using the Hat Creek mm-array, which might be a molecular counterpart of the dust layer observed by Bally et al. (1983) and Felli et al. (1984).

New mapping and analysis techniques for NASA's Kuiper Airborne Observatory are described which permit us to obtain information of size scales of order 10″ in the far-infrared. Basically, the focal-plane image is highly oversampled while the telescope is scanned smoothly and repeatedly over the region of interest with a slit of size λ/D. Maximum-entropy deconvolution is then used to obtain spectral frequency information down to scales of ∼ λ/2D.

Although infrared observations are ideal to study a molecular cloud, an infrared spectrum alone is not enough to determine the physical parameters in the source (Rowan-Robinson 1980). An intensity gradient in sub-millimeter wavelengths was considered by some authors as a measure of the density fall off. But the derived distribution laws are still controversial (Scoville and Kwan 1976, Westbrook et al. 1976, Keene et al. 1982). Other parameters entering the interpretation of the infrared observations are the emissivity and the temperature distribution of the dust. In most models of molecular clouds, major efforts have been devoted to accurately determine the dust temperature for the assumed density gradient and emissivity (Jones and Merrill 1976, Leung 1976, Unno and Kondo 1977, Rowan-Robinson 1980).

Extensive reflection nebulae have been discovered around GGD27 IRS and around W75N IRS by mapping the infrared polarization in the K band.

It was found that the infrared radiation from both objects is extended at λ = 2.2 μm, by using the Agematsu 1-m, the UH 2.2-m, and the UKIR 3.8-m telescopes. We have carried out polarization mapping with the Kyoto polarimeter on the UKIRT in August 1985.

The effect of a strong protostellar wind on a dense molecular cloud with a magnetic field is investigated by time-dependent magnetohydrodynamic calculations which take into account the cooling due to H2 molecules as the dominant one. The shocked region obtained here seems to be responsible for the formation of the bright H2 emission with a high-velocity width observed in the Orion-KL Nebula.

We have performed numerical calculations for both static and dynamic structures of molecular clouds in which stars would be formed. The assumption in our calculations is that a cloud, which is embedded in an external hot and tenuous uniform medium, is isothermal and axisymmetric.

High velocity bipolar gas flows are observed very frequently towards regions of star formation, and it has been conjectured that almost every star of mass larger than 1 M⊙ could undergo a phase of mass ejection during its formation (see e.g. Lada 1985). To explain the collimation of gas flows at interstellar scale, models have been proposed based on a stellar wind or violent isotropic ejection of matter by the protostar, that is pressure collimated by the molecular cloud in which it is embedded (Canto 1980, Königl 1982). In some cases, a molecular disk is observed perpendicular to the direction of the flow, but it is not quite sufficient to collimate it, see for example the high resolution CS observations of Takano et al. (1984) and Kawabe et al. (1984). Also, collimation occurs at a distance smaller than 3x1013m, according to the optical emission line observations of Mundt and Fried (1983).

No one has drawn attention as to whether bipolar jets precess or not. We examine here the possibility of precession of bipolar jets from a theoretical point of view (Fukue and Yokoo 1986).

We first characterize various models proposed for bipolar jets in the light of precession. That is, can they admit precession? If they can, how long is a precessional period P?

A hydromagnetic model is presented for the bipolar flow of molecular gas from newborn stars and for the radio jet emerging out of active galactic nuclei. We assume a tightly-twisted helical magnetic field in the jet, which can collimate and accelerate the gas along the jet axis. The Lorentz force is also shown to rotate the gas around it.

The pinching effect of the magnetic field is studied as a possible mechanism for collimating stellar winds into bipolar flows in star-forming regions. Axisymmetric, steady, polytropic stellar wind models are constructed by solving numerically the magnetohydronynamic equation. The magnetic field is assumed to be radial near the star. Far from the star the magnetic field makes a spiral near the equatorial plane and the toroidal components build up. The pressure and the tension of the toroidal magnetic field deflects the wind away from the equator toward the rotation axis. This deflection continues until the flow becomes nearly cylindrical near the rotation axis. This state is a pinch configuration in which dense gas is confined into a collimated flow by the toroidal magnetic field. This mechanism works under very general circumstances in the magnetic stellar winds from rotating stars.

There is a simple relationship among moment of inertia I, rotational kinetic energy K, and momentum L given by (David Layzer, private communication), 2IK ≧ L. During the Hayashi phase a rotating protostar will amplify the trapped magnetic field by a dynamo-like process. Since the rotation is expected to be fast, many unstable modes will be excited and will grow exponentially in time until some nonlinear processes saturate the amplitude. However, it may happen that the reduction in rotational kinetic energy becomes so large that without increasing the moment of inertia the inequality given above may not be satisfied. The only way to increase the moment of inertia is to move the mass outward. This can be done by transferring the angular momentum outward through the magnetic field. So we will have a fast rotating mass shell at the outer edge of the star. Further transfer of angular momentum will push the shell against the accretion disk; the moving masses of the disk will divert the mass flow along the background magnetic field which extends perpendicular to the accretion disk. This results in the hollow cone jets from both poles because the outward motion is primarily on the equatorial plane.

Uchida and Shibata have proposed the “sweeping-magnetic-twist” mechanism for the formation of astrophysical jets in relation to the accretion disks (disks around protostars, around black hole in the center of active galactic nuclei, and so on) in which a jet is accelerated by the jxB force in the relaxing magnetic twist created in the winding-up of the poloidal magnetic field by the rotation of the contracting disk (Uchida and Shibata 1985a, b; Shibata and Uchida 1986a, b; Uchida et al. 1985). In this mechanism, a jet is collimated also by the jxB force due to the large scale poloidal magnetic field whose footpoints are squeezed in the contracting disk. The main mechanism involved is different from that of centrifugal wind models (Blandford and Payne 1982, Pudritz and Norman 1983) and worked out indepentently, but the centrifugal effect itself is automatically built-in.

As a model of ionized jets from young stars, an analytic solution has been derived from the resistive MHD equations. The essence of our model and an outline of the calculation are presented.

It is observed that a number of large-scale supersonic bipolar flows exist in star forming regions. Infrared sources which seem to excite active motions are usually found in the center of these objects (cf. the recent surveys by Bally and Lada 1983, Torrelles et al. 1983, Snell et al. 1984, Goldsmith et al. 1984). From the observation of the high density gas, the bipolar flow seems to originate from the interaction of the isotropic stellar wind with a large scale flattened interstellar cloud from which the protostars are formed.

We examine the hydrodynamical wind-type jet in the funnel formed along a rotational axis of accretion tori surrounding a proto star, taking into account the gravitational field produced by torus-gas (Fukue and Yamamoto, in press, 1986). In the current models (e.g. Fukue 1982, 1983), an astrophysical jet was assumed to be accelerated along the funnel considering only the gravitational field of the central object.

Recent observations in radio, infrared and visible wavelengths have revealed the presence of small, elongated gaseous structures that appear to emanate from young stars. These structures are frequently interpreted as jets, perhaps similar in nature to those observed in extragalactic objects. We argue that these apparent “jets” could simply be light emitted by, or reflected from the walls of the cavities expected to be formed when the winds of these young stars drive their surrounding gaseous medium away. When viewed from certain positions the radiation from the walls of these cavities appears to the observer as elongated structures. A simple model is presented to illustrate this projection effect.

We have discovered a highly collimated optical jet emanating from a faint star and pointing towards the Herbig-Haro object HH34 (Reipurth 1985, Reipurth et al. 1986).

The statistical properties of winds form young stars are summarized and discussed. One and the same mechanism, possibly related to the process of star formation, appears to be responsible for mass loss in all pre-main-sequence stars. Moreover, evidence is found that the ionization and the acceleration of the winds of very young stars are produced by processes different from those operating in main sequence and more evolved stars.

A model is suggested to explain the variability of the optical structure and the integral brightness of cometary nebulae (CN) occurring at timescales of several years and tens of years (Gyulbudaghian et al. 1977, Cohen et al. 1977, 1981, Magakyan 1981, Gyulbudaghian 1982). A CN is assumed to be a reflection nebula; it is a wall of a conical cavity in the circumstellar gas-and-dust torus illuminated by the central star (Cohen 1974). I explain the CN's variability by the presence of small tilted circumstellar disc of gas-and-dust, located inside the internal channel of the large circumstellar torus (see Figure 1). A similar model was put forward by Ward-Thompson et al. (1985) to account for a tilt angle of about 30° between the direction of short optical jets (stellar wind, channelled by the small disc) and the large-scale bipolar outflow (focused by the large torus) in the CN NGC 6729 associated with the star R CrA. Tilt angles of about 30° between optical and radio structures exist in CN NGC 2261 (Cantó et al. 1981) and GM 1-29 (Levreault 1984).

CRL2688 is suggested to be one of the proto-planetary nebulae which are probably at a stage in which the central star is evolving from the red giant phase with rapid mass loss (Zuckerman 1978). The bipolar shape in both the optical and H2 emission indicates that a dense toroid of dust and gas obscures the star and surrounds the optical emission. The toroid is probably responsible for channelling the mass loss to the polar directions (Ney et al. 1975, Morris 1981, Beckwith et al. 1984). We present the results of mapping observations of CO (J = 1-0) emission from the expanding molecular envelope (Zuckerman et al. 1976, Lo et al. 1976, Knapp et al. 1982, Thronson et al. 1983) of the bipolar reflection nebula CRL2688 using the Nobeyama 45-m telescope with a 1.5″ resolution at a 7″.5 observing spacing.