Pulsar magnetic field for an infinitely conductive accretion disk     

N. R. Sibgatullin  T. A. Doroshenko 《Astronomy Letters》2002,28(11):769-772

The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk.  相似文献   

Ghosts of the Milky Way: a search for topology in new quasar catalogues     

S. J. Weatherley  S. J. Warren  S. M. Croom  R. J. Smith  B. J. Boyle  T. Shanks  L. Miller  M. P. Baltovic 《Monthly notices of the Royal Astronomical Society》2003,342(1):L9-L13

  相似文献   

SN 1999E: another piece in the supernova–gamma-ray burst connection puzzle     

L. Rigon  M. Turatto  S. Benetti  A. Pastorello  E. Cappellaro  I. Aretxaga  O. Vega  V. Chavushyan  F. Patat  I. J. Danziger  M. Salvo 《Monthly notices of the Royal Astronomical Society》2003,340(1):191-196

  相似文献   

Double–double radio galaxies: remnants of merged supermassive binary black holes     

F. K. Liu  Xue-Bing Wu  S. L. Cao 《Monthly notices of the Royal Astronomical Society》2003,340(2):411-416

  相似文献   

Digital photographic photometry of NGC 5253 and NGC 2915     

J. L. Sérsic  C. J. Donzelli 《Astrophysics and Space Science》1992,193(1):87-94

The surface digital photometry for NGC 5253 and NGC 2915 is given. The luminosity profiles and colour gradients are discussed and compared. It is concluded that NGC 2915 differs from NGC 5253, both in the extension and intensity of the star burst event because of the kinematical behaviour of the captured gas.CONICET, Buenos Aires, Visiting Astronomer, Cerro Tololo Inter-American Observatory, La Serena, Chile, operated by NSF  相似文献   

On the relationship between the Apollo 16 ancient regolith breccias and feldspathic fragmental breccias,and the composition of the prebasin crust in the Central Highlands of the Moon     

Randy L. Korotev 《Meteoritics & planetary science》1996,31(3):403-412

Abstract Two types of texturally and compositionally similar breccias that consist largely of fragmental debris from meteorite impacts occur at the Apollo 16 lunar site: Feldspathic fragmental breccias (FFBs) and ancient regolith breccias (ARBs). Both types of breccia are composed of a suite of mostly feldspathic components derived from the early crust of the Moon and mafic impact-melt breccias produced during the time of basin formation. The ARBs also contain components, such as agglutinates and glass spherules, indicating that the material of which they are composed occurred at the surface of the Moon as fine-grained regolith prior to lithification of the breccias. These components are absent from the FFBs, suggesting that the FFBs might be the protolith of the ARBs. However, several compositional differences exist between the two types of breccia, making any simple genetic relationship implausible. First, clasts of mafic impact-melt breccia occurring in the FFBs are of a different composition than those in the ARBs. Also the feldspathic “prebasin” components of the FFBs have a lower average Mg/Fe ratio than the corresponding components of the ARBs; the average composition of the plagioclase in the FFBs is more sodic than that of the ARBs; and there are differences in relative abundances of rare earth elements. The two breccia types also have different provenances: the FFBs occur primarily in ejecta from North Ray crater and presumably derive from the Descartes Formation, while the ARBs are restricted to the Cayley plains. Together these observations suggest that although some type of fragmental breccia may have been a precursor to the ARBs, the FFBs of North Ray crater are not a significant component of the ARBs and, by inference, the Cayley plains. The average compositions of the prebasin components of the two types of fragmental breccia are generally similar to the composition of the feldspathic lunar meteorites. With 30–31% Al₂O₃, however, they are slightly richer in plagioclase than the most feldspathic lunar meteorites (～29% Al₂O₃), implying that the crust of the early central nearside of the Moon contained a higher abundance of highly feldspathic anorthosite than typical lunar highlands, as inferred from the lunar meteorites. The ancient regolith breccias, as well as the current surface regolith of the Cayley plains, are more mafic than (1) prebasin regoliths in the Central Highlands and (2) regions of highlands presently distant from nearside basins because they contain a high abundance (～30%) of mafic impact-melt breccias produced during the time of basin formation that is absent from other regoliths.  相似文献   

Palaeointensity In the Pelagic Realm: Marine Sediment Data Compared With Archaeomagnetic and Lake Sediment Records     

C. G. Constable  L. Tauxe† 《Geophysical Journal International》1987,90(1):43-59

Summary. Four box cores collected from the Ontong—Java plateau during the Eurydice expedition have been used to make relative geomagnetic palaeo-intensity measurements. Rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy, and that they are suitable for relative intensity estimates. These are obtained by normalizing the NRM by an ARM imparted in a low DC bias field. the palaeoceanographic event known as the preservation spike is used to establish a crude time-scale for the record so that it may be compared with other data from the same region, and also with global palaeointensity estimates. the marine sediment data are quite similar to Australian intensity data from lake sediments and archaeomagnetic sources, but as might be expected exhibit some obvious differences from the global record.  相似文献   

Pulsar Wind Nebulae in Egret Error Boxes     

Mallory S. E. Roberts  Crystal L. Brogan  Bryan M. Gaensler  Jason W. T. Hessels  C.-Y. Ng  Roger W. Romani 《Astrophysics and Space Science》2005,297(1-4):93-100

A remarkable number of pulsar wind nebulae (PWN) are coincident with EGRET γ-ray sources. X-ray and radio imaging studies of unidentified EGRET sources have resulted in the discovery of at least six new pulsar wind nebulae (PWN). Stationary PWN (SPWN) appear to be associated with steady EGRET sources with hard spectra, typical for γ-ray pulsars. Their toroidal morphologies can help determine the geometry of the pulsar which is useful for constraining models of pulsed γ-ray emission. Rapidly moving PWN (RPWN) with more cometary morphologies seem to be associated with variable EGRET sources in regions where the ambient medium is dense compared to what is typical for the ISM.  相似文献   

Numerical Modeling of the Largest Terrestrial Meteorite Craters     

B. A. Ivanov 《Solar System Research》2005,39(5):381-409

Multi-ring impact basins have been found on the surfaces of almost all planetary bodies in the Solar system with solid crusts. The details of their formation mechanism are still unclear. We present results of our numerical modeling of the formation of the largest known terrestrial impact craters. The geological and geophysical data on these structures accumulated over many decades are used to place constraints on the parameters of available numerical models with a dual purpose: (i) to choose parameters in available mechanical models for the crustal response of planetary bodies to a large impact and (ii) to use numerical modeling to refine the possible range of original diameters and the morphology of partially eroded terrestrial craters. We present numerical modeling results for the Vredefort, Sudbury, Chicxulub, and Popigai impact craters and compare these results with available geological and geophysical information.  相似文献   

Wavelet Spectrum Analysis Of Eit/Soho Images     

V. Delouille  J. De Patoul  J. F. Hochedez  L. Jacques  J. P. Antoine 《Solar physics》2005,228(1-2):301-321

The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum. We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis.  相似文献