摘要:

The South African Astronomical Observatory is the national observatory for optical and infrared astronomy in South Africa. It has its headquarters in Cape Town and the main telescopes are located at the Sutherland site about 250 km north–east of Cape Town. The facilities include four telescopes ranging from 1.9 m to 0.5 m and are instrumented for optical spectroscopy, CCD imaging, infrared imaging, and optical and infrared photometry. The research carried out with these facilities covers a wide range of stellar and galactic research, with special emphasis on the Magellanic Clouds, the structure of our own Galaxy, pulsating stars, the distance scale, support of space observatory research, and international campaigns. The future development of optical/infrared astronomy in southern Africa is discussed. In particular, the unique contribution that can be made by a southern hemisphere observatory located on the African continent is stressed. Finally we comment on aspects of international collaboration and the educational importance of astronomy. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46995

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The ROSAT (Ro¨ntgensatellit) X‐ray astronomy satellite has completed the first all‐sky x‐ray and XUV survey with imaging telescopes. About 60 000 new x‐ray and 400 new XUV (1) sources were detected. This contribution will deal with preliminary results from the ROSAT ALL‐SKY X‐RAY SURVEY. The ROSAT diffuse and point‐source x‐ray skymaps, the positional accuracy obtained for the x‐ray sources, and a few results from correlations performed with available catalogues in various energy bands like the Radio, Infrared, Visible, UV, and hard x‐rays as well as identifications from optical follow‐up observations will be presented. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46996

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The recent discovery of anisotropies in the cosmic microwave background (CMB) by the Cosmic Background Explorer (COBE) has spurred a high level of activity in cosmology. Having originated at the remotest epochs of the Universe within our reach, the CMB is in fact one of the most accurate probes of the early Universe and thus a powerful test for cosmological models. Limitations and restrictions to the power spectrum of primordial perturbations are derived, taking into account the statistical properties of galactic clustering. Topological analysis of COBE’s anisotropy maps is used to test for the consistency of cosmological models with observations. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46997

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Latest estimates of the three cosmological parameters, the density parameter, Hubble constant and the cosmological constant are discussed, in particular with regard to observational constraints on their possible values. These observational constraints include limits on the density of baryonic matter from Big Bang nucleosynthesis, estimates of mass density from the dynamics of galaxies and clusters, estimates from the ages of globular clusters and nuclear cosmochronology, constraints from the cosmic microwave background, results from infra red galaxy data and radio source data, and possible estimates from gravitational lensing. Estimates of the cosmological parameters from radio source data are hampered by the evolution of radio source properties which is not well understood. An investigation of the effect of assuming a non zero cosmological constant on the linear size evolution of radio galaxies is made. It is found that the inclusion of a non zero cosmological constant does not significantly reduce the amount of linear size evolution in the sample used. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46999

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The quasar/galaxy unification hypothesis based on pure orientation has been investigated using the observed linear size (D)‐luminosity (P) relation for a sample of radio sources at low frequency. It was found that the quasar D‐P slope and intercept exceeded that of radio galaxies by a factor of about 5 and 3, respectively. The observed relation appeared to contradict that expected in a random source orientation hypothesis in which the FRII radio galaxies would be seen as a quasar if their orientation angle is within 44° to the line of sight. The result rather suggested an intrinsic difference in the size distribution between radio galaxies and quasars even at similar luminosities and redshifts. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.47000

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An inelastic collision model is proposed as a plausible mechanism for the production of optical emitting electrons seen in some large scale jets. The target proton density is shown to be readily available through the entrainment of thermal gas as the jets interact and share their momentum with their environment. The optical flux densities predicted by the model for some typical optical jets are in reasonable agreement with the observed values. The model also predicts a relativistic proton flux from the galactic center with spectral index, &Ggr;≤2.0. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.47001

出版商:AIP    

年代:1995

数据来源: AIP