The planetary nebula K 1-2 and its binary central star VW Pyx     

K. M. Exter  D. L. Pollacco  S. A. Bell 《Monthly notices of the Royal Astronomical Society》2003,341(4):1349-1359

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Constraints on a planetary origin for the gap in the protoplanetary disc of GM Aurigae   总被引：1，自引：0，他引：1  

W. K. M. Rice  Kenneth Wood  P. J. Armitage  B. A. Whitney  J. E. Bjorkman 《Monthly notices of the Royal Astronomical Society》2003,342(1):79-85

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Astrometric signatures of self-gravitating protoplanetary discs     

W. K. M. Rice  P. J. Armitage  M. R. Bate  I. A. Bonnell 《Monthly notices of the Royal Astronomical Society》2003,338(1):227-232

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A new simple model for high-frequency quasi-periodic oscillations in black hole candidates   总被引：2，自引：0，他引：2  

L. Rezzolla  S'i. Yoshida  T. J. Maccarone  O. Zanotti 《Monthly notices of the Royal Astronomical Society》2003,344(3):L37-L41

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Comet nuclei: Morphology and implied processes of surface modification     

A.T. Basilevsky  H.U. Keller 《Planetary and Space Science》2006,54(8):808-829

Surface morphology and related issues for nuclei of three comets: Halley, Borrelly and Wild 2, are considered in the paper. Joint consideration of publications and results of our analysis of the comets’ images led to conclusions, partly new, partly repeating conclusions published by other researchers. It was found that typical for all three nuclei is the presence of rather flat areas: floors of craters and other depressions, mesas and terraces. This implies that flattening surfaces or planation is a process typical for the comet nuclei. Planation seems to work through the sublimation-driven slope collapse and retreat. This requires effective sublimation so this process should work only when a comet is close to the Sun and if on the nucleus there are starting slopes, steep and high enough to support the “long-distance” avalanching of the collapsing material. If the surface had no starting slopes, then instead of planation, the formation of pitted-and-hilly surfaces should occur. An example of this could be the mottled terrain of the Borelly nucleus. Both ways of the sublimational evolution on the nucleus surface should lead to accumulation of cometary regolith. The thickness of the degassed regolith is not known, but it is obvious that in surface depressions, including the flat-floor ones, it should be larger compared with nondepression areas. This may have implications for the in situ study of comets by the Deep Impact and Rosetta missions.Our morphological analysis puts constraints on the applicability of the popular “rubble-pile comet nucleus” hypothesis (Weissman, 1986. Are cometery nuclei primordial rubble piles? Nature 320, 242-244.). We believe that the rubble pile hypothesis can be applicable to the blocky Halley nucleus. The Borelly and Wild 2 nuclei also could be rubble piles. But in these cases the “rubbles” have to be either smaller than 30-50 m (a requirement to keep lineament geometry close to ideal), or larger than 1-2 km (a requirement to form the rather extended smooth, flat surfaces of mesa tops and crater floors). Another option is that the Borelly and Wild 2 nuclei are not rubble piles.In relation to surface morphology we suggest that three end-member types of the comet nuclei may exist: (1) impact cratered “pristine” bodies, (2) non-cratered fragments of catastrophic disruption, and (3) highly Sun-ablated bodies. In this threefold classification, the Wild 2 nucleus is partially ablated primarily cratered body. Borrelly is significantly ablated and could be either primarily cratered or not-cratered fragment. Halley is certainly partially ablated but with the available images it is difficult to say if remnants of impact craters do exist on it.Recently published observations and early results of analysis of the Tempel 1 nucleus images taken by Deep Impact mission are in agreement with our conclusions on the processes responsible for the Halley, Borrelly and Wild 2 nuclei morphologies. In particular, we have now more grounds to suggest that decrease in crater numbers and increase of the role of smooth flat surfaces in the sequence Wild 2?Tempel 1?Borelli reflects a progress in the sublimational degradation of the nucleus surface during comet passages close to the Sun.  相似文献   

On the orbits and masses of the satellites of the Pluto-Charon system     

Man Hoi Lee  S.J. Peale 《Icarus》2006,184(2):573-583

Two small satellites of Pluto, S/2005 P1 (hereafter P1) and S/2005 P2 (hereafter P2), have recently been discovered outside the orbit of Charon, and their orbits are nearly circular and nearly coplanar with that of Charon. Because the mass ratio of Charon-Pluto is ∼0.1, the orbits of P2 and P1 are significantly non-Keplerian even if P2 and P1 have negligible masses. We present an analytic theory, with P2 and P1 treated as test particles, which shows that the motion can be represented by the superposition of the circular motion of a guiding center, the forced oscillations due to the non-axisymmetric components of the potential rotating at the mean motion of Pluto-Charon, the epicyclic motion, and the vertical motion. The analytic theory shows that the azimuthal periods of P2 and P1 are shorter than the Keplerian orbital periods, and this deviation from Kepler's third law is already detected in the unperturbed Keplerian fit of Buie and coworkers. In this analytic theory, the periapse and ascending node of each of the small satellites precess at nearly equal rates in opposite directions. From direct numerical orbit integrations, we show the increasing influence of the proximity of P2 and P1 to the 3:2 mean-motion commensurability on their orbital motion as their masses increase within the ranges allowed by the albedo uncertainties. If the geometric albedos of P2 and P1 are high and of order of that of Charon, the masses of P2 and P1 are sufficiently low that their orbits are well described by the analytic theory. The variation in the orbital radius of P2 due to the forced oscillations is comparable in magnitude to that due to the best-fit Keplerian eccentricity, and there is at present no evidence that P2 has any significant epicyclic eccentricity. However, the orbit of P1 has a significant epicyclic eccentricity, and the prograde precession of its longitude of periapse with a period of 5300 days should be easily detectable. If the albedos of P2 and P1 are as low as that of comets, the large inferred masses induce significant short-term variations in the epicyclic eccentricities and/or periapse longitudes on the 400-500-day timescales due to the proximity to the 3:2 commensurability. In fact, for the maximum inferred masses, P2 and P1 may be in the 3:2 mean-motion resonance, with the resonance variable involving the periapse longitude of P1 librating. Observations that sample the orbits of P2 and P1 well on the 400-500-day timescales should provide strong constraints on the masses of P2 and P1 in the near future.  相似文献   

城市地理数据生产及应用调查与评估分析   总被引：1，自引：1，他引：0  

孔云峰  刘欣亮 《地球信息科学学报》2006,8(3):7-11

国内城市地理数据开发和应用水平差异很大,且不少城市面临诸多困难和挑战。本文使用问卷调查和案例分析的方法评估城市地理数据的开发和应用水平,为城市地理数据资源开发和持续利用提供战略建议。同时分析了地理空间数据的基本特征,强调了地理数据的重要性,提出反映地理空间数据生产与应用水平的关键指标,如专业人才与组织、数据投资与预算、数据生产与供应、数据标准与质量、空间数据基础设施、数据法令与政策、数据应用与效益、数据共享程度、成功应用数目等,建议依据这些基本要素构建评估指标体系。最后提出了城市地理空间数据生产与应用调查的组织、方法和程序,并建议政府主管部门或行业协会尽快展开有关工作。  相似文献   

A charge-coupled device study of high-latitude Galactic structure: testing the model parameters     

S. Karaali  S. G. Ak  S. Bilir  Y. Karata&#;  G. Gilmore † 《Monthly notices of the Royal Astronomical Society》2003,343(3):1013-1024

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可持续发展进程中的政府能力建设     

芮国强 《广东海洋大学学报》2003,23(2):72-78

可持续发展作为现代化建设的两大战略之一 ,对我国政府的能力提出了挑战。可持续发展战略的实施 ,要求加强政府的作用 ,将政府建设成为强有力而又廉价的政府。为此 ,我国政府应从加强政府的财政汲取能力建设、强化中央政府协调地区发展的能力 ,加强政府调控能力建设、强化中央政府协调当前利益和长远利益、经济利益与生态效益的能力 ,并从根本上转变政府职能、精兵简政、建设廉价高效的政府等方面着手来提高我国政府推进和实施可持续发展战略的能力  相似文献   

An atlas of the optical spectrum of supernova 1987A in the large magellanic cloud     

V. J. Mclntyre  A. C. Gilmore  J. B. Hearnshaw 《Journal of Astrophysics and Astronomy》1990,11(1):81-123

Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements of selected lines in the spectra  相似文献