We have performed multiepoch single-telescope and Very Long Baseline Interferometry (VLBI) observations of an anomalously strong outburst of a water vapor maser in the Orion KL region that occurred in 1998. This burst, dubbed a superburst, exhibited a flux density increase that started in 1997 December and reached a maximum of 4.6 × 106 Jy in 1998 September; it then decreased to 0.2 × 106 Jy in 1999 February. The spatial and the velocity structure revealed by our observations showed that the bursting feature consisted of at least two components having two different peak velocities. Moreover, these two components exhibited a relative motion over 287 days with the relative position of the two components changing across the period of the outburst maximum. This suggests that an overlapping of two maser clouds caused the superburst. The brightness temperature reached 1016 K, while the line width was as narrow as 0.48 km s-1 at maximum phase. This extremely high brightness and narrow line width can be understood as the radiation from the maser being highly beamed.

The superfine structure of the H2O supermaser region in Orion KL was investigated in 1982-1985. The brightness temperatures were found to be T-b < 10(16) K. The distribution of the components and their velocities correspond to the model of an expanding ring. For the protostar mass 1 M-circle dot, the inner ring radius is 15 AU, and the rotation velocity is 9 km/s. The emission of the inner parts of the ring in a window of 0.5 km/s is amplified by more than a factor of 100 by an outer shell with a rotation velocity of 7.6 km/s. A chance to detect the disk components in other velocities is very much lower.

We have studied the superfine structure of the active H2O maser region in Orion KL with an angular resolution of ≤ 0.3 × 0.7 mas. The high level of H2O maser emission from 1979-1988 was due to an accretion disk, which is divided into five groups of protoplanetary rings. The peak brightness temperatures of the structures was Tpeak = 1013-14 K. The region is located in the OMC-1 molecular cloud, VLSR ⋍ 7.74 km/s. The cloud amplifies by more than two orders of magnitude the emission from the structures, whose radial velocities are within the maser window ±0.3 km/s. Due to this, the velocity of the H2O super maser emission is constant. In the quiescent period of 1995 a 6 AU jet was discovered, PA = −32°, Tb ⋍ 1011K. In 1998 the jet's brightness temperature increased by more than 3 orders of magnitude. Initially the jet's position angle was PA = −45°, and then changed to PA = −38°. During the period of decreasing emission in 1999 the jet had changed its form and became a helix, that suggests the precession of the rotation axes. In the central part of the jet there is a compact bright source - “the ejector” - with Tejc = 1017 K.

The fine structure of active regions in Orion KL has been studied. It is shown that accretion disks and bipolar outflows accompany star formation. The accretion disks are divided into protoplanetary rings. The H2O super maser emission is associated with the rings and bipolar outflows. The surrounding medium (V-LSR=7.74 km/s) amplifies the emission within the maser window by more than two orders of magnitude.

On May 26, 1995, we studied the region of H2O supermaser emission in Orion KL in a "quiescent" period by using VLBA with an angular resolution of 0.3 x 0.7 mas. We detected a jet and two compact features. This bipolar structure complements the previously discovered star-accretion disk system. The jet is 5.5 x 0.5 AU in size, and its position angle is PA = -33 degrees. The brightness temperature of the bipolar structure is T-b approximate to 10(12) K. The radio flux density of the jet is F = 1060 Jy. The emission exhibits a linear polarization that reaches 45%.

This paper presents very high dynamic range VLBI observations of the quasar 3C345 at 18 cm wavelength at two epochs, 1981.11 and 1985.27. We find that the direction of the jet changes drastically and the surface brightness decreases with increasing distance from the core. We show that a true three-dimensional curvature of the jet in space is needed to obtain the observed decrease of intensity with distance from the core, both in an adiabatic expansion model as well as in a model where the comoving flux is constant. Our observations confirm the detection of a previously reported low surface brightness component, C0. In addition, there is a large component extended perpendicular to the jet axis which we associate with a stationary shock at a distance consistent with the expected position of the narrow line region. Models for the intensity of the jet fitted to the observed dependence of intensity with distance from the core suggests this shocked region to be the place where the jet is expanding adiabatically after having had a constant width closer to the core. A limit on the allowed viewing angle theta less-than-or-similar-to 40-degrees is derived from the lack of any detectable counterjet.

The two-sided radio structure associated with the S5-quasar 1928+738 (z = 0.30) has been mapped at 408 and 1662 MHz with MERLIN, at resolutions of 1.5 and 0.2 arcsec, respectively. A geometrical and kinematical description of the curved jets is investigated in terms of a precessing beam model; moderate intrinsic brightness asymmetry of the jets has to be invoked to account for the apparent brightness ratio of jet to counterjet. This comparatively low ratio seems to contradict the existence of a one-sided milliarsecond scale jet that has been reported to display superluminal motion. The mass scale jet structure may consist of boosted filaments embedded in a broad cylindrical jet

We present an EVN map at 1.67 GHz and combined EVN-MERLIN maps at 1.67 and 5 GHz of the compact steep-spectrum radio source 3C147. The maps reveal three dominant extended regions and a bright core. The structure cannot be readily explained with the standard relativistic beaming model. A sharp bend in the VLBI jet, and the overall distorted structure may be caused by the interaction of the jet with ambient gas, though we cannot rule out a multiengine source each with its own jet. Physical parameters of the knots along the VLBI jet and the age of 3C147 have been estimated.

AbstractA space project for studying ecological Earth problems is being carried out by means of radio techniques. A 30 m prototype antenna has already been deployed and tested. The radio telescope will be launched in 1994 into a circular orbit haying an altitude 600 km and an inclination of 65°. The planned mission time is ≥ 1.5 year; 25% of this will be available for VLBI observations at wavelengths 6 and 18 cm.

Results are reported of the measurement of balloon motion in the upper layers of the Venus atmosphere. The measurement of the balloon trajectories was carried out by differential very-long-baseline interferometry (VLBI) observations of the balloons relative to the fly-by spacecrafts (VEGA-1 and VEGA-2). Balloon-2, launched in the southern hemisphere of the planet led to the discovery of gas motion with average velocities of 65.3 m s-1 and 3.4 m s-1 in longitude and latitude, respectively. Balloon-1, launched in the northern hemisphere, showed that gas motions occur with an average velocity of 68.7 m s-1 in the longitudinal direction, but no wind was detected in the latitudinal direction. Pendulum motion of the balloon baskets with a period of 7.4 s was detected on many occasions. This occurred 10 times more frequently in the southern hemisphere than in the northern one. The nature of these phenomena is discussed.

The region of the H2O megamaaer emission in Orion KL had been studied by VLBI method. The structure is a chain of the compact components oriented under the angle X ≅ −80°. The size of the components is ⩽ 0.1 A.U., the brightness temperature Tb ≅ 1017 K, the linewidth of each component is Δ f ⋜ 7 kHz. The emission has linear polarization P ⋝ 80 % and position angle is changed by 9.2 degree / A.U. The velocity of the components has a gradient 0.41 km/sec A.U. The masers are unsaturated, the kinetic temperature Tk ≤ 120 K. The structure corresponds to an expanding protoplanet rings, radius of which is equal R = 6 A.U. The rotation and the expanding velocities are equal 5 and 3.8 km/s accordingly. Mass of a protostar is ~ 0.7 M⊙.

We present the first VLBI observations using the Ooty telescope. An array consisting of telescopes at Ooty (India), Crimea (USSR), Torun (Poland), Westerbork (Netherlands) and Jodrell Bank (United Kingdom) was operated in 1983 December at a frequency of 327 MHz. Nearby galaxies, compact quasars and SS433 were observed in this pilot experiment. Most of the galaxies were found to be well resolved. The structure of SS433 (visible only on the shortest baseline) is consistent with that obtained in previous high-frequency VLBI work. The visibilities of the compact quasars indicate that large-scale scattering may be taking place in the interplanetary medium.

The structure of the quasar 3C 345 has been studied at 18 and 49 cm wavelengths by VLBI method. The structure has a nucleus and a jet, which changes direction with distance from the nucleus. The continuum emission of the nucleus and the jet regions correspond to a source with a large optical depth, the cut frequence goes down with increasing distance from nucleus.

MERLIN and VLA maps of the OH masers around OH/IR stars show that their characteristic double-peaked spectrum is caused by an expanding shell of material ejected from the star. In order to investigate the compact structure of the OH masers within this shell we have observed two such OH/IR stars (OH 127.8 and 104.9) using the European VLBI network. The resulting VLBI aperture synthesis maps are the first to be made of OH/IR stars. In each case, the maps show compact sources on the nearside of the shell, but no corresponding source on the far side of the shell. This is interpreted in terms of amplification of the stellar thermal emission and a mechanism for this process is outlined.

view Abstract Citations (98) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Proper motions and distances of H2O maser sources. III - W51NORTH Schneps, M. H. ; Lane, A. P. ; Downes, D. ; Moran, J. M. ; Genzel, R. ; Reid, M. J. Abstract Accurate relative positions of the W51NORTH masers, determined by VLBI observations of the water vapor maser emission at 22 GHz, show changes of a few milli-arcsec over a two-year period. These displacements are interpreted as the result of transverse motions of about 50 km/sec, comparable with the radial velocity dispersion for this source, which are not random and show that clusters of maser features travel as a unit. The members of the maser cluster seem to be embedded in cloudlets of molecular gas having a scale size of 5 x 10 to the 14th cm. B-alpha observations made to establish the ambient velocity of the W51 region show that the ambient LSR velocity of the H II region is consistent with the molecular cloud velocity of about 56 km/sec. The distance to W51NORTH is estimated to be 8.3 + or - 2.5 kpc. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159267 Bibcode: 1981ApJ...249..124S Keywords: Gas Flow; Interstellar Gas; Interstellar Masers; Molecular Clouds; Supersonic Flow; Water Masers; Emission Spectra; H Ii Regions; Molecular Gases; Nebulae; Stellar Evolution; Very Long Base Interferometry; Astronomy full text sources ADS |

Utilizing a large number of published observations, we investigate the detailed structure of the Crab Nebula over a range of wavelengths from 35 mm to 75 em, and identify many different features. The spectra of some of these features are followed to longer wavelengths, extending to nearly 10 m. Physical conditions within the features are discussed.