Vistas in Astronomy最新文献

A brief account is given of the development and status of the Australian Long Baseline Array (LBA), with particular emphasis on recent developments and milestones. Major improvements are scheduled in the near future as part of the Major National Research Facilities (MNRF) programme and the LBA will be operated as a National Facility.

Observations of the radio emission at 15 GHz from GRS 1915+105 were made with the Ryle telescope intermittently during late 1995, early 1996, at a time when the source was active in the X-ray band. Wide variations in flux density were observed during the flaring activity. On several days when the flux was at an intermediate level there appeared to be a quasi-periodic component with a period close to 40 min. Later observations show that other periods are also present.

We present high dynamic range total intensity and linear polarization images of the CSS quasar 3C309.1 obtained with the VLBA at 5 and 8.4 GHz. The standard model of CSS objects is that they are embedded in a dense environment that de-polarises the source at longer wavelengths. We find little de-polarization associated with the jet. Only the core is significantly de-polarized. We also do not find the strong gradients in rotation measure across the source that are expected in the standard model. The integrated polarization properties of the source are due to a combination of the core polarization changing rapidly with frequency and a steep spectrum jet. In addition to being a CSS object, this radio source is believed to be embedded in an extremely massive cooling flow, which should generate very large rotation measures. We find rotation measures consistent with those found in ordinary quasars, a few hundred radians per meter square in the rest frame of the source. About 40 mas from the core, the jet is disrupted and appears to inflate a small radio lobe similar to that found in FRII sources but on a much smaller scale.

We present some of the results from mapping the turnover frequency, turnover flux and magnetic field distributions in the parsecscale jets of 3C 273 and 3C 345. We discuss the existing problems of VLBI image analysis related to the extraction of spectral information.

We present results of observations of the BL Lac objet 1219 + 285 with the European VLBI Network (EVN) at 1.7 GHz and 5.0 GHz. Our data reveal a misalignment of ∼60° between the radio structure of 1219 + 285 observed at these two frequencies. The lower resolution (∼20 mas) structure seen with the EVN at 1.7 GHz appears to be orientated in a direction intermediate between that of the inner VLBI jet and that of the outer VLA jet, indicating continuity of the jet from milliarcsecond to arcsecond scales.

We describe results obtained in prototyping a Kohonen self-organising feature map as a user interface to a large document collection. We then discuss the provision of various tools which will be used in quality control of databases and catalogs produced from, and cross-referenced with, the online astronomical literature; and which will be used in future information seeking and processing intelligent agent technologies.

I propose a method of inferring the geometry of the obscuring material in radio-loud active galaxies by examining the relationship between the inferred nuclear extinction and the core-to-lobe radio flux ratio. I use Monte Carlo simulations to estimate the quality of data expected from such a project and examine its usefulness in discriminating between alternative structures.

The LEDA extragalactic database is managing 35,841 images obtained by a direct ‘post-stamp’ digitization of the Palomar Sky Survey between δ = −33° and δ = 85°. These images are used to recognize automatically LEDA galaxies and to get their main parameters. So, a catalog of 28,00 galaxies is built. This process constitutes the first step of an new one which can lead to an automatic feeding of LEDA. The next step is the recognition of new galaxies. Some experiments have been done using Neural Network algorithm. These tests are briefly discussed.

It is known that hard X-rays emission is a good indicator of the intrinsic luminosity of Seyfert 2s in those cases where they are transmitted through the torus, rather than seen purely by reflection as in NGC 1068. It has recently been demonstrated that the [OIII] λ5007 line emission and hard X-rays emission in Seyfert 2s follow the same correlation as found for Seyfert 1s, and hence that [OIII] flux can also be used to infer the intrinsic power. Recent models predict that the inner regions of the torus have hot dust with a black body peak around 3.5 μm (L-band). We use comparisons of the hard X-ray, [OIII] and L-band properties of PG quasars, Seyfert 1 and 2 galaxies, to infer the amount of reddening in the latter. Our values for the extinction are compared with those inferred from the hard X-ray column densities.

Symmetry plays a remarkable role in perception problems. For example, peaks of brain activity are measured in correspondence with visual patterns showing symmetry. Relevance of symmetry in vision was already noted by Köler in 1929. Here, properties of a symmetry operator are reported and a new algorithm to measure local symmetries is proposed. Its performance is tested on segmentation of complex visual patterns and the classification of sparse images.