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The BN/KL area in the Orion molecular cloud is a model for the study of star formation. The main source of outflow in the BN/KL area could be an object termed radio source I, which is thought to be surrounded by rotating molecular material. High-resolution observations of silicon monoxide (SiO) and water maser emission are reported from gas around source I, and it is shown that the area is dominated by a conical bipolar outflow within 60 AU of the source.

Accurate measurements of extragalactic distances is required for realistic descriptions of the age, geometry and fate of the Universe. A geometric distance to the galaxy NGC4258 is reported, taken from direct measurements of orbital motions in the gas disk around the nucleus of the galaxy. The distance, 7.2 plus or minus 0.3 Mpc is more precise than any extragalactic distance yet measured.

Baseline interferometric observations of OH masers in the galactic star-forming complex W49N provide evidence for magnetic-field-induced anisotropy of the interstellar medium. The elliptical maser images show perpendicular alignment to the galactic plane. This maser orientation indicates that the magnetic field of our galaxy mediates energy transfer from large to small spatial scales, thereby effecting interstellar turbulence.

The extra fine structure of the active region of H2O supermaser emission of Orion KL (angular resolution is 0.1 mas) is studied. A central body / accretion disk / bipolar outflow / bullets / envelope is discovered, that corresponds to the earliest stage of the small-mass star formation. The ejector – a compact bright source ≤0.05 AU, Tb ≈1017K. The bipolar outflow, vej≈10 km/s is a highly-collimated stream with a ration length/diameter ∼ 60, rotation period is ∼ 0.5 yr, precession period ∼10 yrs, precession angle ∼ 33°. Precession forms a conical helix jet. The envelope amplified radio emission by about three orders of magnitude at velocity at v=7.65 km/s. [ABSTRACT FROM AUTHOR]

Observations of the starburst galaxy, M82, have been made with a 20-station global very long-baseline interferometry (VLBI) array at λ18 cm. Maps are presented of the brightest young supernova remnants (SNR) in M82 and the wide-field mapping techniques used in making images over a field of view of ∼1 arcmin with 3-milliarcsecond resolution are discussed. A limit has been placed on the power-law deceleration of the young supernova remnant (SNR) 43.31+592 with an index greater than 0.73±0.11 from observations with the European VLBI Network. Using the global array we have resolved compact knots of radio emission in the source which, with future global observations, will enable better constraints to be placed on the expansion parameters of this SNR. The latest global observations have also provided high-resolution images of the most compact radio source in M82, 41.95+575. We determine an upper limit to the radial expansion rate along the major axis of 2000 km s[sup -1]. However, the new images also show structure resembling that of collimated ejection which brings into question the previous explanation of the source as being a result of the confinement of a supernova by a high-density circumstellar medium. It is apparent that we are now able to image the brightest supernova remnants in M82 with a linear scale which allows direct comparison with galactic SNR such as Cassiopeia A. [ABSTRACT FROM AUTHOR]

We studied the growth of the shell-like radio structure of supernova SN 1993J in M 81 from September 1993 to October 2003 with very-long-baseline interferometry (VLBI) observations at the wavelengths of 3.6, 6, and 18 cm. We developed a method to accurately determine the outer radius (R) of any circularly symmetric compact radio structure such as SN 1993J. The source structure of SN 1993J remains circularly symmetric (with deviations from circularity under 2%) over almost 4000 days. We characterize the decelerated expansion of SN 1993J until approximately day 1500 after explosion with an expansion parameter \(m = 0.845 \pm 0.005 (R \alpha t^m)\). However, from that day onwards the expansion differs when observed at 6 and 18 cm. Indeed, at 18 cm, the expansion can be well characterized by the same m as before day 1500, while at 6 cm the expansion appears more decelerated, and is characterized by another expansion parameter, \(m_6 = 0.788 \pm 0.015\). Therefore, since about day 1500 onwards, the radio source size has been progressively smaller at 6 cm than at 18 cm. These findings differ significantly from those of other authors in the details of the expansion. In our interpretation, the supernova expands with a single expansion parameter, \(m = 0.845 \pm 0.005\), and the 6 cm results beyond day 1500 are caused by physical effects, perhaps also coupled to instrumental limitations. Two physical effects may be involved: (a) a changing opacity of the ejecta to the 6 cm radiation, and (b) a radial decrease of the magnetic field in the emitting region. We also found that at 6 cm about 80% of the radio emission from the backside of the shell behind the ejecta is absorbed (our average estimate, since we cannot determine any possible evolution of the opacity), and the width of the radio shell is \((31 \pm 2) %\) of the outer radius. The shell width at 18 cm depends on the degree of assumed absorption. For 80 % absorption, the width is \((33.5 \pm 1.7) %\), and for 100 % absorption, it is \((37.8 \pm 1.3) %\). A comparison of our VLBI results with optical spectral line velocities shows that the deceleration is more pronounced in the radio than in the optical. This difference might be due to a progressive penetration of ejecta instabilities into the shocked circumstellar medium, as also suggested by other authors., Astronomy

We have studied the fine structure of the active H[sub 2]O supermaser emission region in Orion KL with an angular resolution of 0.1 mas. We found central features suggestive of a bipolar outflow, bullets, and an envelope which correspond to the earliest stage of low-mass star formation. The ejector is a bright compact source ≤0.05 AU in size with a brightness temperature T[sub b] ≅ 10[sup 17] K. The highly collimated bipolar outflow ∼30 has a velocity v[sub ej] ≅ 10 km s[sup –1], a rotation period of ∼0.5 yr, a precession period of ∼10 yr, and a precession angle of ∼33°. Precession gives rise to a jet in the shape of a conical helix. The envelope amplifies the radio emission from the components by about three orders of magnitude at a velocity v=7.65 km s[sup –1].© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Reports the details of a study which attempted to calculate the absolute distance to the galaxy NGC4258. Measurements basis on the orbital motions in a disk of gas surrounding the nucleus of the galaxy; Use of absolute distance in calculating the age, geometry and fate of the Universe; Estimated distance to NGC4258; Role of this estimation in future distance-scale calibrations.