Vistas in Astronomy最新文献

The angular resolution of ∼ 0.15 arcsec (∼ 10 pc), achieved by MERLIN, is ideal for investigation of neutral gas in the nuclei of nearby Seyferts on scales of < 10 pc. We present, here, such observations of the radio source associated with the nucleus of NGC4151. We find that only the component containing the nucleus shows significant absorption, whereas no measurable absorption is seen against other components within the 4 arcsec radio jet. There is structure in the absorption on scales as small as 0.1 arcsec, with column densities in excess of 6 × 10²¹ atoms cm⁻² over parts of the radio nucleus. The neutral hydrogen column densities are much higher than UV absorption measurements which implies that the optical/UV continuum nucleus is not coincident with the strongest radio component. We suggest that the radio nucleus is associated with a weak VLBI component which is ∼ 0.1 arcsec (∼ 7 pc) to the west of the deepest absorption. We deduce that any neutral hydrogen torus, in which the nucleus is embedded, can be no thicker than 50 pc and may have a linear (E-W) extent of < 40 pc.

SKY Online //www.skypub.com is the World Wide Web site of Sky Publishing Corporation, publisher of Sky & Telescope magazine. Conceived mainly as an electronic extension of the company's marketing and promotion efforts, SKY Online has also proven to be a useful tool for communication between amateur and professional astronomers.

This paper describes the planning by ICSU Press and UNESCO leading to a Conference of Experts on Electronic Publishing in Science held in Paris in February 1996. The origin of the conference arose from a resolution at the 1993 General Assembly of the International Council of Scientific Unions. The experiences and views of expert scientists, librarians, publishers and information brokers are summarized together with their recommendation formulated by working groups and approved by the 150 invited participants drawn from 34 countries worldwide. In conclusion, an attempt is made to show the relevance of these deliberations to the aims of the 1996 workshop on Converging Computing Methodologies in Astronomy.

The angular asymmetries and relative separations of the hot-spots of FRII radio sources in a complete sample of 3CR sources have been used to study the effects of misalignment of the directions of ejection and the velocities of the hot-spots, in conjunction with a test of Barthel's models which unify radio galaxies and quasars. It is found that the observed distributions of asymmetry angles in radio galaxies and quasars are consistent with unified models, and with the source components being ejected uniformly within an angle of 6–7° about the source axis. The separation quotients are also consistent with the scheme if the velocities of the hot-spots have a broad distribution about a mean of 0.2c, with values extending at least up to 0.4c.

The hard-edged ionization cone seen by the HST imaging of NGC 4151 and the line-of-sight gas observed in some Seyfert 1 galaxies present a strong challenge for the simplest version of the Unified Model of AGN, which predicts that bi-conically shaped EELR can be observed only in type 2 objects and the line-of-sight to type 1 nucleus must be clear. To accommodate these rather contradictory requirements we suggest a modification of the shadowing/obscuration scenario. In our model the collimation of the ionizing radiation is provided by a partially neutral atmosphere surrounding the physically thin, dense torus. This atmosphere provides a natural way of producing wide angle ionization cones and at the same time allows for a relatively clear view of the central regions for some angles outside the cone edges. The model has an observationally testable predictions. Recently discovered nuclear disks in some elliptical galaxies hosting AGN may provide a natural way of supplying the gas for both the torus and the atmosphere surrounding it.

We report on high spatial and spectral resolution observations of the distribution, physical parameters and kinematics of the molecular interstellar medium toward the nuclei of three nearby active galaxies. The data consist of high resolution interferometric observations of the HCN and CO J = 1 → 0 lines, single dish observations of several mm/submm isotopic lines of HCN and CO, and subarcsecond resolution imaging spectroscopy of the near-IR K-band.

We have used the Nordic Optical and the William Herschel Telescopes to obtain images and long-slit spectra of Cygnus A under conditions of sub-arcsecond seeing. The high spatial resolution and accurate positional information obtained from a comparison between the images and spectra allow us to study in detail the kinematics and excitation of the extended ionized gas. Strong velocity gradients and complex line profiles are detected in positions close to the radio axis corresponding to the emission line clouds recently resolved by HST. The results are interpreted in terms of a strong interaction between the radio jet and the interstellar medium.

This paper deals with edge-preserving restoration. It is well known that quadratic regularization results in smoothing edges and ringing artefacts. The goal of this paper is to present edge preserving deterministic regularization for image restoration. We first focus on the design of edge preserving regularizing functions and their properties about edge modeling. Then we propose a deterministic algorithm in order to mimimize the non quadratic criterion. Finally some results on restoration of the Hubble space telescope images are shown.

In the simple unified model for Seyfert nuclei, type 2 Seyferts are those where direct view of the central source is blocked by a dusty molecular torus. This simple model is able to explain many observed properties of Seyfert nuclei but fails to explain the UV excess observed in the continuum of many type 2 Seyferts, the relatively low level of continuum polarization, and the undiluted near IR stellar absorptions. The simplest solution is to postulate a continuum source on top of the scattered nuclear one. I discuss here some of the implications of having young stars in the torus providing the additional continuum.