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311.
Luis Floría 《Celestial Mechanics and Dynamical Astronomy》1997,68(1):75-85
We study the possibilities and limitations of the application of generalized Delaunay-like transformations (in the 6-dimensional
phase space) and TR-like mappings (in the 8-dimensional, extended phase space) to perturbed two-body problems with a time-varying
Keplerian parameter μ(t), that is, to Gylden-type systems. For the sake of theoretical completeness, both negative- and positive-energy
motion (with nonstationary coupling parameter) are, in principle, considered. Our developments are intended to introduce canonical
variables parallelling the classical ones of Delaunay and the Delaunay-Similar variables of Scheifele.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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We study the excitation of density and bending waves and the associated angular momentum transfer in gaseous discs with finite thickness by a rotating external potential. The disc is assumed to be isothermal in the vertical direction and has no self-gravity. The disc perturbations are decomposed into different modes, each characterized by the azimuthal index m and the vertical index n , which specifies the nodal number of the density perturbation along the disc normal direction. The n = 0 modes correspond to the two-dimensional density waves previously studied by Goldreich & Tremaine and others. In a three-dimensional disc, waves can be excited at both Lindblad resonances (LRs; for modes with n = 0, 1, 2, … ) and vertical resonances (VRs; for the n ≥ 1 modes only). The torque on the disc is positive for waves excited at outer Lindblad/vertical resonances and negative at inner Lindblad/vertical resonances. While the n = 0 modes are evanescent around corotation, the n ≥ 1 modes can propagate into the corotation region where they are damped and deposit their angular momenta. We have derived analytical expressions for the amplitudes of different wave modes excited at LRs and/or VRs and the resulting torques on the disc. It is found that for n ≥ 1 , angular momentum transfer through VRs is much more efficient than LRs. This implies that in some situations (e.g. a circumstellar disc perturbed by a planet in an inclined orbit), VRs may be an important channel of angular momentum transfer between the disc and the external potential. We have also derived new formulae for the angular momentum deposition at corotation and studied wave excitations at disc boundaries. 相似文献
314.
M. Vannier R. G. Petrov B. Lopez F. Millour 《Monthly notices of the Royal Astronomical Society》2006,367(2):825-837
We present the high angular resolution technique of colour-differential interferometry for direct detection of extrasolar giant planets (EGPs). The measurement of differential phase with long-baseline ground-based interferometers in the near-infrared could allow the observation of several hot giant extrasolar planets in tight orbit around the nearby stars, and thus yield their low- or mid-resolution spectroscopy, complete orbital data set and mass. Estimates of potentially achievable signal-to-noise ratios are presented for a number of planets already discovered by indirect methods. The limits from the instrumental and atmospheric instability are discussed, and a subsequent observational strategy is proposed. 相似文献
315.
J. C. Muzzio D. D. Carpintero F. C. Wachlin 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):173-190
We created a triaxial stellar system through the cold dissipationless collapse of 100,000 particles whose evolution was followed
with a multipolar code. Once an equilibrium system had been obtained, the multipolar expansion was freezed and smoothed in
order to get a stationary smooth potential. The resulting model was self-consistent and the orbits and Lyapunov exponents
could then be computed for a randomly selected sample of 3472 of the bodies that make up the system. More than half of the
orbits (52.7 % ) turned out to be chaotic. Regular orbits were then classified using the frequency analysis automatic code
of Carpintero and Aguilar (1998, MNRAS 298(1), 1–21). We present plots of the distributions of the different kinds of orbits projected on the symmetry planes of
the system. We distinguish chaotic orbits with only one non-zero Lyapunov exponent from those with two non-zero exponents
and show that their spatial distributions differ, that of the former being more similar to the one of the regular orbits.
Most of the regular orbits are boxes and boxlets, but the minor axis tubes play an important role filling in the wasp waists
of the boxes and helping to give a lentil shape to the system. We see no problem in building stable triaxial models with substantial
amounts of chaotic orbits; the difficulties found by other authors may be due not to a physical cause but to a limitation
of Schwarzschild’s method. 相似文献
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320.
Yang Zongrang 《地球科学与环境学报》1997,(1)
在分析了近年来秦、祁、昆造山带研究中部分成果资料的基础上,认为商、丹主缝合线以南的杨子古陆北缘区早古生代由于一系列“三叉”裂谷系的发育而曾沿布尔汉布达山─略阳─山阳─线打开一次洋盆,致使南秦岭─柴达木-带从扬子陆块北缘分离出来,一度成为一独立微古陆块向北漂移;古生代有其独特的演化历史。而当时主洋盆北侧的华北古陆南缘区则发育有完整的沟、弧、盆体系.面貌很象今天的太平洋西海岸。 相似文献