Search

Through analysis of correlations within the longitude-velocity distribution of 6.7-GHz methanol masers, we identify density enhancements indicative of large-scale regions of enhanced star formation. In the context of the inner structure of our Galaxy these are interpreted as the starting points of the spiral arms and the interaction of the long Galactic bar with the 3–kpc arms. Signatures of a continuous 3–kpc arm structure are seen including a prominent tangent at –22° Galactic longitude.

We present a series of 8.4-GHz very-long-baseline radio interferometry images of the nucleus of Centaurus A (NGC5128) made with a Southern Hemisphere array, representing a 3.33-year monitoring effort. The nuclear radio jet is [approximate]50 milliarcseconds in extent, or at the 3.5-megaparsec distance of NGC5128, [approximate] 1 parsec in length. Sub-luminal motion is seen and structural changes are observed on time scales shorter than 4 months. High-resolution observations at 4.8 and 8.4 GHz made in November 1992 reveal a complex morphology and allow us to unambiguously identify the self-absorbed core located at the southwestern end of the jet.

The study of high-resolution radio observations of second Galactic superluminal radio source GRO J1655-40 reveals the relativistic motion between two components of the radio source. The two components are moving away from each other at speeds, greater than that of the speed of light. This relativistic motion between the two objects is attributed to the ejection of material from these two astronomical objects, at relativistic speeds in the course of accretion into a blackhole.

In the early days of methanol maser discoveries, the 92–101 A+ transition at 23.1 GHz was found to exhibit maser characteristics in the northern star-forming region W3(OH) and probable maser emission in two other sources. Attention subsequently turned to the 6.6-GHz 51–60 A+ methanol maser transition, which has proved a valuable tracer of early high-mass star formation. We have undertaken a new search for 23.1-GHz methanol masers in 50 southern star formation regions using the Parkes radio telescope. The target sources all exhibit class II methanol maser emission at 6.6 GHz, with 20 sources also displaying maser features in the 107.0-GHz 31–40 A+ methanol line. Strong emission at 23.1 GHz in NGC 6334F was confirmed, but no emission was detected in the remaining sources. Thus the 23.1-GHz methanol masers are rare. A maser model in which methanol molecules are pumped to the second torsionally excited state by radiation from warm dust can account for class II maser activity in all the transitions in which it is observed. According to this model the 23.1-GHz maser is favoured by conditions representing low gas temperature, high external dust temperature, low gas density and high column density of methanol; the scarcity of this maser indicates that such combinations of conditions are uncommon. We have undertaken new model calculations to examine the range of parameters compatible with the upper limits on 23.1-GHz emission from our survey. Further constraints apply in sources with upper limits to maser emission at 107.0 GHz and the combination of data for the two transitions delineates a narrow range of gas density and methanol abundance if the dust temperature is 175 K or greater. While the results are subject to the uncertainties of the chosen model, they may be applicable to the majority of methanol maser sites in the vicinity of newborn high-mass stars, in which methanol masers other than the 6.6- and 12.1-GHz transitions are not detected. [ABSTRACT FROM AUTHOR]

We have used the Australian Long Baseline Array (LBA) to produce milliarcsecond images of five sites of methanol (CH3OH) maser emission at 6.7 GHz. These are all sites that have linear morphologies at arcsecond resolutions, which have been hypothesized to be due to the masers forming in edge-on circumstellar discs. We find that a simple disc model cannot explain the observations. We discuss various alternatives, and suggest a new model that explains how linear velocity gradients can be produced in methanol masers that arise in planar shocks propagating nearly perpendicular to the line of sight. [ABSTRACT FROM AUTHOR]

We have used the Australia Telescope National Facility Mopra 22-rn rnillimetre telescope to search for emission from the 85.5-GHz 6[SUB-2]-7[SUB-1] E and 86.6-GHz 7[SUB2]-6[SUB3] A[SUP-] transitions of methanol. The search was targeted towards 22 star formation regions which exhibit maser emission in the 107.0-GHz 3[SUB1]-4[SUB0] A[SUP-] rnethanol transition, as well as in the 6.6-GHz 5[SUB1]-6[SUB0] A[SUP+] transition characteristic of class II methanol rnaser sources. Each of these regions was searched at 85.5 GHz, resulting in five detections, of which one appears to be a newly discovered maser. For the 86.6-GHz transition, observations were made of 18 regions, which yielded two detections, but no new maser sources. This search demonstrates that emission from the 6[SUB-2]-7[SUB-1] E and 72-63 A[SUP-] transitions is rare. Detection of maser emission from either of these transitions therefore indicates the presence of special conditions, different from those in the majority of methanol maser sources. We have observed temporal variability in the 86.6-GHz emission towards 345.010+1.792, which -- along with the very narrow line width -- confirms that the emission is a maser in this source. We have combined our current observations with published data for the 6.6-, 12.1-, 85.5-, 86.6-, 107.0-, 108.8- and 156.6-GHz transitions for comparison with the maser model of Sobolev & Deguchi. Both detections and non-detections are useful for setting limits on the physical conditions in star-forming regions which contain methanol maser emission. This has allowed us to estimate the likely ranges of dust temperature, gas density and rnethanol column density, both for typical methanol maser sources and for those sources which also show 107.0- GHz emission. The gas temperature can also be estimated for those sources exhibiting masers at 85.5 and/or 86.6 GHz. [ABSTRACT FROM AUTHOR]

We report molecular line observations of the G34.26+0.15/34.24+0.13 complex, which contains a bright molecular core and a proto-B-star. ATCA observations show that both objects are closely associated with 6.7 GHz class II, methanol masers. Methanol line series at 96, 157 and 241 GHz towards the protostar position were observed at SEST. Modelling of the methanol data shows that the molecular core embedding protostar is not greatly influenced by the outflow form the young stellar object. Molecular line mapping at Onsala reveals the presence of a cavity and two compact clumps to the southeast of the bright molecular core. The protostar is situated at the edge of the one compact clump. It is very likely that the material out flowing from the protostar freely escapes towards the cavity. Comparison of the line profiles of different molecules shows substantial chemical inhomogeneity within the region. [ABSTRACT FROM AUTHOR]

We have used the Australia Telescope Compact Array (ATCA) to make a sensitive (5σ≃100 mJy) search for maser emission from the 4765-MHz [sup 2]Π[sub 1/2]F=1→0 transition of OH. 55 star formation regions were searched and maser emission with a peak flux density in excess of 100 mJy was detected toward 14 sites, with 10 of these being new discoveries. In addition we observed the 4750-MHz [sup 2]Π[sub 1/2]F=1→1 transition towards a sample of star formation regions known to contain 1720-MHz OH masers, detecting marginal maser emission from G348.550-0.979. If confirmed this would be only the second maser discovered from this transition. The occurrence of 4765-MHz OH maser emission accompanying 1720-MHz OH masers in a small number of well-studied star formation regions has led to a general perception in the literature that the two transitions favour similar physical conditions. Our search has found that the presence of the excited-state 6035-MHz OH transition is a much better predictor of 4765-MHz OH maser emission from the same region than 1720-MHz OH maser emission is. Combining our results with those of previous high-resolution observations of other OH transitions we have examined the published theoretical models of OH masers and find that none of them predicts any conditions in which the 1665-, 6035- and 4765-MHz transitions are inverted simultaneously. [ABSTRACT FROM AUTHOR]

Examines the methanol masers and molecular shock tracers in the W3(OH) and W3(H[sub 2]O) region with the BIMA array and Onsala 20meter radiotelescope. Characteristics of the outflows in the region; Construction of a model for the W3(OH) methanol maser formation; Increase of maser emission spikes in a high density.

We have used the ATNF Mopra antenna and the SEST antenna to search in the directions of several class II methanol maser sources for emission from six methanol transitions in the frequency range 85–115 GHz. The transitions were selected from excitation studies as potential maser candidates. Methanol emission at one or more frequencies was detected from five of the maser sources, as well as from Orion KL. Although the lines are weak, we find evidence of maser origin for three new lines in G345.01+1.79, and possibly one new line in G9.62+0.20. The observations, together with published maser observations at other frequencies, are compared with methanol maser modelling for G345.01+1.79 and NGC 6334F. We find that the majority of observations in both sources are consistent with a warm dust (175 K) pumping model at hydrogen density ∼10[sup 6] cm[sup -3] and methanol column density ∼5×10[sup 17] cm[sup -2]. The substantial differences between the maser spectra in the two sources can be attributed to the geometry of the maser region. [ABSTRACT FROM AUTHOR]

A southern hemisphere survey of methanol emission sources has been carried out using the Australia Telescope National Facility Mopra millimetre telescope. 85 sources, the majority of them masers, have been detected in the 8[sub 0]-7[sub 1] A[sup +] transition of methanol at 95 GHz. Together with a similar northern hemisphere survey, this completes the search for 95-GHz methanol emission from the Galactic plane. The previously found correlation between intensities of methanol emission at 44 and 95 GHz is confirmed here with the larger sample of sources. The results of large velocity gradient statistical equilibrium calculations confirm the classification of these sources as class I methanol masers pumped through collisional excitation. [ABSTRACT FROM AUTHOR]