Modelling the 10-image lensed system B1933+503     

S. Nair 《Monthly notices of the Royal Astronomical Society》1998,301(2):315-322

A gravitational lens model is presented for the newly discovered 10-image system B1933+503. The underlying object, revealed by modelling, is a triple radio source on the scale of a couple of hundred mas that is well-aligned along the line of sight with a foreground and somewhat flattened lensing galaxy, the orientation and location of which match those of an observed galaxy, known to be at a redshift of 0.755. Uncertainties in the modelling are obtained by a Monte Carlo exercise. Observational tests of the lens model are proposed, and the time delays between various pairs of images are determined, as the core of the source is known to be significantly variable. Future observations of the lens hold the key to using B1933+503 to constrain Hubble's constant. Despite the absence of a source redshift, the utility of the system as a probe of the structure of the lens galaxy is unparalleled as it provides a surfeit of easily identifiable constraints for modelling the system.  相似文献   

A timing formula for main-sequence star binary pulsars     

Norbert Wex 《Monthly notices of the Royal Astronomical Society》1998,298(1):67-77

In binary radio pulsars with a main-sequence star companion, the spin-induced quadrupole moment of the companion gives rise to a precession of the binary orbit. As a first approximation one can model the secular evolution caused by this classical spin-orbit coupling by linear-in-time changes of the longitude of periastron and the projected semi-major axis of the pulsar orbit. This simple representation of the precession of the orbit neglects two important aspects of the orbital dynamics of a binary pulsar with an oblate companion. First, the quasiperiodic effects along the orbit, owing to the anisotropic 1/ r ³ nature of the quadrupole potential. Secondly, the long-term secular evolution of the binary orbit, which leads to an evolution of the longitude of periastron and the projected semi-major axis, which is non-linear in time.   In this paper a simple timing formula for binary radio pulsars with a main-sequence star companion is presented which models the short-term secular and most of the short-term periodic effects caused by the classical spin-orbit coupling. I also give extensions of the timing formula that account for long-term secular changes in the binary pulsar motion. It is shown that the short-term periodic effects are important for the timing observations of the binary pulsar PSR B1259–63. The long-term secular effects are likely to become important in the next few years of timing observations of the binary pulsar PSR J0045–7319. They could help to restrict or even determine the moments of inertia of the companion star and thus probe its internal structure.   Finally, I reinvestigate the spin-orbit precession of the binary pulsar PSR J0045–7319 since the analysis given in the literature is based on an incorrect expression for the precession of the longitude of periastron. A lower limit of 20° for the inclination of the B star with respect to the orbital plane is derived.  相似文献   

参数调整对气象预测的B-P网络模型性能的影响     

邓新民  顾永刚 《成都信息工程学院学报》1998,(1)

为了探索ＢＰ网络的参数调整特性,进行了参数α、β的选取对ＢＰ算法的收敛速度和模型的稳定性的影响研究。通过ＢＰ网络用于气象预测建模的参数调整个例分析表明：参数α、β的取值对ＢＰ模型的稳定性无显著影响,但参数值的调整尤其是β值的调整对建模的收敛速度有明显的影响。  相似文献   

Mathematical Modelling and Accuracy Testing of Spot Level 1B Stereopairs     

M. J. Valadan Zoej  & G. Petrie 《The Photogrammetric Record》1998,16(91):67-82

During a project concerned with DEM generation using SPOT stereoscopic imagery, difficulties were experienced when using Level 1B stereopairs for the task. This paper presents a mathematical solution to overcome this problem which has been implemented at the University of Glasgow. Results are included from experimental tests which were carried out over a test field in Jordan using this solution. These tests used five SPOT Level 1B stereopairs together with a single SPOT Level 1A stereopair for comparative purposes. The residual errors at the ground control points and independent check points are given and show that a satisfactory solution was achieved.  相似文献   

陕西段家坡黄土剖面中布容／松山古地磁界线附近铱异常的发现及其启示   总被引：3，自引：0，他引：3  

马配学  侯泉林 《地质学报》1998,72(2):173-177

利用高灵敏度放射化学中子活化分析方法,对我国陕西段家坡黄土剖面早－中更新统（约０．７３Ｍａ）沉积界线附近铱和其它元素的丰度进行了测定。结果表明,在布容／松山（Ｂ／Ｍ）古地磁界线附近铱的含量明显增大,最大值为４６．３ｐｇ／ｇ。相对于整个剖面的平均背景值（约１５ｐｇ／ｇ）大约富集了３倍。用地壳元素钪进行标准化之后,铱异常十分明显,而其它元素在界线附近则没有变化。黄土剖面上铱异常的赋存层位与西南太平洋钻  相似文献   

Y11B航空物探(电/磁)综合站西北找水初步成果   总被引：1，自引：1，他引：0  

孟庆敏 《物探与化探》1998,22(4):241-246

1997年9月23日～10月8日,在甘肃省安西—敦煌地区用Y11B航空物探(电/磁)综合站和GPS导航定位进行了地下水勘查试生产工作。用均匀大地模型,结合已知的水文地质资料,初步圈定了淡水区、过渡类型水区、咸水区和苦水区及泉水湖。所推断的水质和土壤含盐量与大的水文地质单元和1:20万水文地质普查报告都吻合得很好,且细节更为清楚。对差异较大的地方做了分析和解释。  相似文献   

翡翠的成因及宝石学意义刍论   总被引：1，自引：0，他引：1  

马婷婷  廖宗廷 《上海国土资源》1998,(2):43-48

从地质学角度出发,对翡翠的成因作了初步研究。以此研究结果为基础,探讨了翡翠的矿床类型,翡翠矿床的找矿方向及翡翠“B”货的科学鉴定。  相似文献   

The C/CO ratio in B335 and the decaying dark matter neutrino hypothesis     

Murphy  Little  & Kelly 《Monthly notices of the Royal Astronomical Society》1998,294(4):635-641

C¹⁸O J  = 2–1, C¹⁷O J  = 2–1 and [C  I ] ³P₁–³P₀ emission from the dense cold cloud B335 has been observed and modelled in order to determine the C/CO ratio. The observed ratio is compared with a prediction by Tarafdar who assumes a mechanism in which the CO dissociation is caused by photons of energy ∼ 13.8 eV. These were postulated by Sciama to result from the decay of dark matter neutrinos. Our value for the C/CO ratio sets an upper limit to the strength of the neutrino decay dissociation process, thus providing a significant datum for interstellar chemistry theory.  相似文献   

A complete infrared Einstein ring in the gravitational lens system B1938 + 666     

L.J. King  N. Jackson  R.D. Blandford  M.N. Bremer  I.W.A. Browne  A.G. de Bruyn  C. Fassnacht  L. Koopmans  D. Marlow  P.N. Wilkinson 《Monthly notices of the Royal Astronomical Society》1998,295(2):L41-L44

We report the discovery, using NICMOS on the Hubble Space Telescope , of an arcsec-diameter Einstein ring in the gravitational lens system B1938+666. The lensing galaxy is also detected, and is most likely an early-type galaxy. Modelling of the ring is presented and compared with the radio structure from MERLIN maps. We show that the Einstein ring is consistent with the gravitational lensing of an extended infrared component, centred between the two radio components.  相似文献   

Equivalent width, shape and proper motion of the iron fluorescent line emission from molecular clouds as an indicator of the illuminating source X-ray flux history     

R. Sunyaev  & E. Churazov 《Monthly notices of the Royal Astronomical Society》1998,297(4):1279-1291

Observations of the diffuse emission in the 8–22 keV energy range, elongated parallel to the Galactic plane, and detection of the strong 6.4-keV fluorescent line with ∼ 1 keV equivalent width from some giant molecular clouds (e.g. Sgr B2) in the Galactic Centre region suggest that the neutral matter of these clouds is (or was) illuminated by powerful X-ray radiation, which gave rise to the reprocessed radiation. The source of this radiation remains unknown. A transient source close to the Sgr B2 cloud, or a short outburst of the X-ray emission from a supermassive black hole at the Galactic Centre are the two prime candidates under consideration. We argue that a new generation of X-ray telescopes combining very high sensitivity and excellent energy and angular resolutions would be able to discriminate between these two possibilities when studying time-dependent changes of the morphology of the surface brightness distribution, the equivalent width and the shape of the fluorescent line in Sgr B2 and other molecular clouds in the region. We note also that detection of broad and complex structures near the 6.4-keV line in the spectra of distant AGNs, which are X-ray weak now, may prove the presence of violent activity in the central engines of these objects in the past. Accurate measurements of the line shape may provide information on the time elapsed since the outburst. Proper motion (super- or subluminal) of the fluorescent radiation wave front can give additional information on the location of the source. Observations of the described effects can provide unique information on the matter distribution inside Sgr B2 and other giant molecular clouds.  相似文献