Serpens is a region of low mass star formation where the magnetic field seems to play a fundamental role. The major axis of the Serpens outflows are aligned with the magnetic field. The most outstanding object in the region is the Serpens Reflection Nebula, SRN. This is characterized by a rather complex bipolar structure with several knots of gas and dust embedded in both nebular lobes. The western lobe is directed out of the cloud toward the observer. The SRN is illuminated by the PMS star Serpens/SVS 2. The star is surrounded by a dust disk; the polarization pattern of the disk can be interpreted as produced by dust grains aligned by the magnetic field frozen-in with the disk.

In Figure 1, we present a map of the polarization of background starlight in the Perseus region (Goodman, Bastien, Myers, and Menard 1989) superposed on contours of integrated 13CO emission (Bachiller and Cernicharo 1986). The polarization vectors map the plane-of-the-sky field (B⊥), assuming as usual that the observed polarization is the result of selective extinction by magnetically aligned dust grains associated with the molecular clouds between the observer and background stars (e.g. Dolginov 1989).

We have detected interstellar polarization amounting to 2.6 % in the Ursa Major molecular clouds at a distance of 110 pc. Assuming that paramagnetic grains in those clouds are aligned with the magnetic fields and combining our results with the measurement of Zeeman splitting at 21 cm (Heiles 1989), we argue the strength and direction of magnetic fields.

We have measured the linear polarization of 8 bright Herbig Ae/Be stars in UBVRI bands. No unique wavelength dependence of polarization magnitude as well as direction is found in these measurements.

Imaging polarimetry has shown that extended objects within star forming clouds may appear polarised due to passage of the light through an intervening region of magnetically aligned dust grains. Two such objects are considered here.

Infrared polarimetry is one of the most useful methods to delineate the magnetic field structure in dark clouds and star-forming regions, where the intracloud extinction is so large that optical polarimetry is inaccessible. We have been conducting a near-infrared polarization survey of background field stars and embedded sources toward nearby dark clouds and star-forming regions (Tamura 1988). Particularly, the magnetic field structure in the denser regions of the clouds are well revealed in Heiles Cloud 2 in Taurus, ρ Oph core, and NGC1333 region in Perseus (Tamura et al. 1987; Sato et al. 1988; Tamura et al. 1988). This survey also suggests an interesting geometrical relationship between magnetic field and star-formation: the IR polarization of young stellar sources associated with mass outflow phenomena is perpendicular to the magnetic fields. This relationship suggests a presence of circumstellar matter (probably dust disk) with its plane perpendicular to the ambient magnetic field. Combining with another geometrical relationship that the elongation of the denser regions of the cloud is perpendicular to the magnetic field, the geometry suggests that the cloud contraction and subsequent star-formation have been strongly affected by the magnetic fields. Thus, it is important to study the universality of such geometrical relationship between IR polarization of young stellar sources and magnetic fields. In this paper, we report the results on a 2 micron polarization survey of 39 T Tauri stars, 8 young stellar objects and 11 background field stars in Taurus dark cloud complex.

We have obtained radio continuum observations of an HH object, known as the “streamer” in Orion using the VLA in a number of configurations at λ2, 6 and 20cm. This object is located several arc-minutes to the north of HH34 in L1641 cloud and exhibits a remarkably long and narrow structure with dimensions of 5′ × 10′ in optical photographs unlike the morphology of any other HH object. Based on radio continuum observations, we have detected a significant linearly polarized emission at λ6cm from the core of the streamer indicating highly uniform magnetic field geometry. This unusual result suggests that the source responsible for producing the nebulosity is a nonthermal-emitting radio source. Because of the presence of a number of newly born low-mass stars in L1641 and because of the detection of a highly reddened 2μm source coincident with the synchrotron source, it is likely that the source at the core of the streamer is a low-mass star responsible for the non-thermal emission and the HH nebulosity. Presence of synchrotron emission associated with a newly born star supports further view that the magnetic field plays a strong role in the early phase of star formation.

The highly collimated H-H flows and “jets” from young stellar objects have in some cases be reported to occur parallel to the direction of the interstellar magnetic field. In order to examine the reality and universality of the apparent connection between the H-H flows and the interstellar field, we compared the position angles of all H-H flows for which (1) the flow direction is well known from monochromatic images, and where (2) the local field direction can be derived unambiguously from interstellar polarization data. The result is given in Figure 1. A more detailed description of these results will be published elsewhere (Appenzeller 1989, Proc. 4th IAP Astrophysics Meeting, P. Delache et al. eds., Paris 1989).

Molecular hydrogen emission lines are associated with collimated outflows from young stellar objects. They have been measured near Herbig–Haro objects within jets as well as at the jet termination. Similarly to HH objects, the lines are produced from radiative shocks which may be in the form of oblique internal jet shocks or bow shocks. A J-shock can only be invoked in a dynamical model context since the H2 lines are often wide (> 30 km s−1). The alternative is the MHD C–shock in which the ionisation level is sufficiently low so that the magnetic field and ions interact weakly with the neutrals. We have investigated C-shock flows by employing approximate forms for the ion-neutral drag, cooling and other processes with the following results.

Different astrophysicai contexts (e.g. extragalactic jets, star forming regions) are related with collimated ouflows. An analysis of this phenomenology in principle would require a fully numerical treatment, however analytical investigations are also possible by assuming a suitable behaviour of streamlines. In this framework we investigate solutions of the hydrodynamic and MHD equations describing helicoidal collimated outflows from a central gravitating object.

A simple but general theory for the formation and propagation of non-relativistic jets is derived from the basic equations of ideal magnetohydrodynamics.

Many objects have been observed that are excited by shocks, but nevertheless do not form a shell shape in a variety of astrophysical environments such as in protostellar and circumstellar medium or as seen in optical jets, H-H objects, and GGD objects. The models for these objects, which have been proposed for explaining observed spectrum, can be divided to two types. First one is the cloudlets interaction model (e.g., Schwartz 1978; Norman and Silk 1979; Raga, Böhm, and Solf 1986). Second one is the radiative jet model in which the knotty structure associated in some H-H objects can be suggested as the shock of Mach disks in “underexpanded” jets (e.g., Mundt 1985; Hartigan 1989). However, the wiggles and the irregular knots have been observed in some H-H objects (e.g., knots; HH33, HH40, and wiggles; HH12, HH7-11), which could not be explained well by the two models above. On the other hand, from the observations for maser emissions in star forming regions, the strong magnetic field is inferred(e.g., Fiebig and Gusten 1989). The magnetic field seems to be important for the dynamical motion in star forming regions. Then, a magnetohydrodynamical reconnection model for these phenomena is investigated. We consider the interaction between dense magnetized cloudlet and wind from the central star, through an 2-D MHD code with the MacCormack-Doner cell hybrid scheme to well represent shock phenomena as well as advective phenomena. The density contours and magnetic field lines of numerical results for γ=5/3 and 1.1 are shown in figure (a) and (b), respectively. We present two case for γ=5/3 and 1.1. Results show that the compression effects related to the adiabatic indexes γ are important in the shocked region. The interaction between the cloudlet and wind induces the bow shock around the cloudlet and elongated magnetic structure in the downstream direction, which is similar between two cases. However, the downstream flow patterns behind the cloudlet are different for each other. For γ=1.1, we have a jet-like structure in downstream region. This is induced by magnetic reconnection with strong compressed effects which produces secondary plasma acceleration. This magnetic reconnection is fast (Patscheck) type, which have been well studied for the model of the earth magne-tospheric substorm, related to the slow shock formation and the strong plasma jet generation (e.g. Sato and Hayashi 1979). Furthermore, these behavior is similar to the disconnection events of comets (Alfvén 1957, Niedner 1980), which suggests us the knots in HH objects can be explained as some separated reconnection points in which the magnetic energy is released explosively. For real interstellar medium, γ=5/3, however, we must consider the effect of radiative cooling (Spitzer 1978). This cooling seems to be important for outflows in the star forming regions (Hanami and Sakashita, 1987) Then, we can interpret the compression effect with small γ as that of the cooling, approximately. This compression mechanism related to the cooling effect in interstellar and magnetic reconnections are important for interpreting the formation, and the structure, and the dynamics of optical jets, H-H objects, and GGD objects.

We report on preliminary numerical MHD simulations of magnetic disk accretion surrounding a compact protostar in which the disk and the hydromagnetic wind interact self-consistently. We show that an outflow is indeed produced, but that its properties are sensitive to the assumed initial poloidal magnetic field structure. In particular, we reconcile the apparently disparate models of Pudritz and Norman (1983,1986) and Uchida and Shibata (1985) concerning the mass ejection mechanism.

Results from models of the chemical evolution at the interfaces between hot, highly-ionized, stellar winds and cool, weakly-ionized, molecular clumps are presented.

We have begun a project to produce self-consistent 2-D MHD simulations of the generation and collimation of mass outflows from star forming regions. We describe our code development work, and present preliminary results.

We show that axisymmetric magnetized winds emanating from rotating stars, disks, tori, etc. generally tend to collimate along the symmetry axis and conjecture that this is the reason there are so many bipolar flows and jets. The actual form of the flows at large distances from the source are either cylindrical or paraboloidal depending on the total poloidal current.

Direct numerical simulations of decaying two-dimensional incompressible MHD flows at Reynolds numbers of several thousands are reported here, using resolutions of 10242 collocation points on a uniform grid. Spatial derivation is performed using Fourier decomposition, assuming periodic boundary conditions, and nonlinear terms are computed in configuration space. The time-stepping scheme is semi-implicit, Crank–Nicolson and third-order Runge–Kutta. The magnetic Prandtl number is equal to unity in all runs. Both deterministic and random initial conditions are used, concentrated in the large scales, with quasi–equipartition between kinetic and magnetic energy. The dynamic range in amplitude of the fields is 107, ensuring well–resolved current and vorticity sheets, over roughly 20 grid points. This leaves sufficient space for tearing instabilities to develop, embedded in a turbulent flow.

We have studied the high energy physical process related to the cosmic ray acceleration for SN1987A. The X-ray flare observed by Ginga satellite (Makino 1988) and TeV γ-rays reported by the JANZOS collaboration (Bond et al. 1988) occurred in January, 1988. These events may be explained by the interaction of the supernova ejecta with the surrounding cloud, which induces the thermalization of shocked material and the acceleration of cosmic ray on the reverse shock at the front of cloud. Especially, the soft X-ray emission from SN1987A is well described by the interaction model of the ejecta with the circumstellar medium (Masai et al. 1988, and Yoshida and Hanami 1988). It seems to be natural to consider that the origin of the γ-ray is connected with that of the X-ray flare, since they had occurred at same time. Then, we consider about the relation of this acceleration mechanism and the evolution scenario of the progenitor.

Existing radiofrequency data on the center of the Galaxy are used to defend the hypothesis that the magnetic field within a radius of at least 70 pc of the nucleus has a poloidal geometry, is relatively uniform in strength, and is very strong relative to extended fields measured elsewhere in the Galaxy, having a flux density greater than or about a milligauss. The implications of this strong, pervasive field are: 1) that a strong ring current is present at radii beyond 70 pc, and 2) that the dynamics of molecular clouds in the Galactic center are significantly affected by, though probably not dominated by, the magnetic field. At radii within 5 pc, far-IR polarization data suggest a substantial deviation of the magnetic field from a poloidal geometry, at least within the gas and dust layer. There, the coupling of the field to the rapidly orbiting gas near the nucleus is presumably responsible for this local distortion of the larger-scale field geometry.

High frequency polarization observations reveal the existence of a poloidal magnetic field structure in the Galactic Centre region on scales of about 200 pc. At lower frequencies large non–thermal spurs are seen tracing the magnetic field up to kpc distances from the Galactic Centre.