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1.
Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF31, were discovered, librating about the L5 Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ7, to be a Trojan, associated with the L4 Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND43) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW15 and 2000 TG2, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion. 相似文献
2.
Magnetars are the neutron stars with the highest magnetic fields up to 1015–1016 G. It has been proposed that they are also responsible for a variety of extra-galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low-mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars. 相似文献
3.
Time scales of the transition from contact binary systems of the W UMa type to single stars of the blue straggler type are estimated. A model of one-way mass transfer from the primary component to the companion inside a common envelope (Eggen et al.) and a model of a contact binary lying on the zero-age main sequence with a companion that is losing mass (F. van't Veer) are used to calculate these scales. The merging times of components were calculated for 304 contact systems of the W UMa type from the Catalog of Approximate Photometric and Absolute Elements of Eclipsing Variable Stars on a scale of loss of mass and orbital angular momentum due to magnetic braking, under the assumption of synchronization of the axial rotation and orbital revolution. On the basis of the resulting statistics, the characteristic merging scales are 0.4-0.6 and 0.5-0.7 Gyr, respectively, for the above two models. The results of a comparison with the work of other authors are discussed. 相似文献
4.
分析了上两个世纪发生在淮河的洪水事件的可公度性，根据其可公度值及其黄金分割点指出1991年与2003年淮河洪水的不可避免，最后讨论了可公度性的局限及淮河洪水可公度值的可能机制。 相似文献
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6.
We present a numerical method for inverting long-period components of lightcurves of asynchronous binary asteroids. Data of five near-Earth binary asteroids, (175706) 1996 FG3, (65803) Didymos, (66391) 1999 KW4, (185851) 2000 DP107 and (66063) 1998 RO1, for two of them from more than one apparition, were inverted. Their mutual orbits' poles and Keplerian elements, size ratios, and ellipsoidal shape axial ratios were estimated via this inversion. The pole solutions and size ratios for 1999 KW4 and 2000 DP107 are in a good agreement with independent estimates from radar measurements. We show that uncertainties of estimates of bulk densities of binary systems can be large, especially when observed on short arcs. 相似文献
7.
Pavel Mayer Marek Wolf P. G. Niarchos K. D. Gazeas V. N. Manimanis Drahomír Chochol 《Astrophysics and Space Science》2006,304(1-4):39-41
New precise times of minimum light for several early-type eclipsing binaries were obtained at three observatories. The changes of period of the following measured binaries are discussed: V1182 Aql, LY Aur, SZ Cam, FZ CMa, QZ Car, LZ Cen, V606 Cen, AH Cep and TU~Mus. 相似文献
8.
This paper deals with the observed variation in the flattening of galaxies with the density of galaxies in the subclusters
of Coma surrounding NGC 4889, NGC 4874, and NGC 4839 based on data from the Abastumani Combined Catalog of Galaxies. The mean
values of the observed ratios of the diameters of the galaxies, as well as histograms of their distributions, indicate that
in the central, dense regions of the subclusters within a volume of 0.5h
75
−1
Mpc3, E and S0 type galaxies are close to spheroidal. A significant reduction in the mean values of the diameters of the galaxies
in the subclusters is noted, regardless of their morphology relative to the galaxies in the halo of the Coma cluster. In the
subclusters, spiral galaxies are found with a hydrogen deficit that is more than 5 times the hydrogen deficit in spirals within
the halo of the cluster. According to their 3-D coordinates, most of the galaxies with a hydrogen deficit are located closer
to the south-east edge of the subcluster surrounding NGC 4874 near an extended gas filament in the x-ray region. This may
indicate that the subcluster is moving toward a central condensation of faint galaxies in the Coma cluster and a possible
merger with it.
__________
Translated from Astrofizika, Vol. 50, No. 3, pp. 355–368 (August 2007). 相似文献
9.
Influences of the mass, moment of inertia, rotation, absence of stability in the atmosphere and some other parameters of neutron stars on the evolution of pulsars are examined. It is shown that the locations and evolutions of soft gamma repeaters, anomalous X-ray pulsars and other types of pulsar on the period versus period derivative diagram can be explained adopting values of B < 1014 G for these objects if they have smaller mass (e.g. about 0.5 Solar mass) compared to the conventionally adopted values of mass. This approach gives the possibility to explain many properties of different types of pulsar. 相似文献
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V.S. Kalantonis E.A. Perdios A.E. Perdiou O. Ragos M.N. Vrahatis 《Astrophysics and Space Science》2003,288(4):479-488
The techniques used for the numerical computation of families of periodic orbits of dynamical systems rely on predictor-corrector
algorithms. These algorithms usually depend on the solution of systems of approximate equations constructed from the periodicity
conditions of these orbits. In this contribution we transform the root finding procedure to an optimization one which is applied
on an objective function based on the exact periodicity conditions. Thus, the determination of periodic solutions and families
of such orbits can be accomplished through unconstrained optimization. In this paper we apply and compare some well-known
minimization methods for the solution of this problem. The obtained results are promising.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
V. Belokurov M. G. Walker N. W. Evans G. Gilmore M. J. Irwin M. Mateo L. Mayer E. Olszewski J. Bechtold T. Pickering 《Monthly notices of the Royal Astronomical Society》2009,397(4):1748-1755
We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope (MMT). From this, we derive a luminosity of M v =−2.5 , a half-light radius of 34 pc and a systemic velocity of ∼−40 km s−1 . Our data also provide evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighbouring fields. We resolve the velocity dispersion of Segue 2 as 3.4 km s−1 and the possible stream as ∼7 km s−1 . This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites – survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts z > 10 and are good candidates for fossils of the reionization epoch. 相似文献
13.
500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical Radio Telescope,FAST)是一个超大口径的可动望远镜,有三项技术创新,一是选址,二是轻型馈源索支撑,三是主动反射面。在主动反射面上,单元面板的面型和面板的出厂加工精度对电磁波在反射面的汇聚有很大影响。FAST主反射面由4 600块三角形反射面板拼接而成,每块面板为边长11 m三角形,这对FAST反射面面板的测量技术提出了更高的要求。摄影测量直接在影像上进行量测,无需接触物体本身;所摄影像信息丰富,可以从中获得所研究物体的大量几何信息和物理信息;适用于大范围、多目标测量,效率高。目前世界上最大的射电望远镜,如GBT和ARECIBO都是采用摄影测量技术进行反射面面形检测。在对现有的面型检测技术调研并试验后,提出基于数字近景摄影测量的方法,对FAST反射面11 m单元面板的面型进行检测,数分钟完成反射面板面型的一次检测,测量精度达到2.5 mm,经过调整后的单元面板的面型精度达到了3.0 mm,结果表明摄影测量应用于FAST反射面单元面板面型检测是可行的。 相似文献
14.
V. A. Shefer 《Celestial Mechanics and Dynamical Astronomy》1990,49(2):197-207
A review is presented of the author's results on application of regularizing and stabilizing KS- transformation in the problem of investigation of the motion of unusual minor planets and comets. Two models of the motion of a minor body are considered, viz. the perturbed two body problem and the perturbed restricted three body problem. The variational equations in KS-variables and transformations for obtaining the matrix of partial derivatives of the instantaneous physical parameters of motion with respect to their initial values are presented. The peculiarities of the implementation of the algorithms developed as programs on a computer are described. The original results of the investigation of the efficiency of the developed algorithms and programs are discussed using as an example the motion of unusual minor planets Icarus and Geographos as well as comets Halley, Honda-Mrkos-Pajdusakova and Gehrels 3. 相似文献
15.
Marykutty Michael 《Planetary and Space Science》2008,56(13):1696-1702
Aerosols are very important in the Martian climate system. Aerosols get charged by the attachment of ions in the atmosphere. Charging of aerosols reduces the conductivity of the atmosphere as the very mobile ions are lost during the ion-aerosol attachment. During a dust storm the dust opacity increases and more ion-aerosol attachment process occurs and consequently conductivity reduces further. It was found that with the background aerosols (dust opacity ∼0.2), the conductivity close to the surface of Mars was reduced by a factor of 5, but during the dust storm (opacity ∼5) of 2001 the conductivity decreased by about 2 orders of magnitude. 相似文献
16.
We analyzed the spectrum of a coronal condensation observed during the total eclipse of 1983 June 11. Under the assumption of rotational symmetry we found the distributions of the electron density and the temperature. The electron density was higher in the centre of the condensation than on the edge. From different line pairs the maximum electron density was found to be between 1.7 3.5×109cm−3 while the temperature was found to be basically uniform at 1.7 2.7×106K. The turbulence velocity was 15 35km/s. The systematic flow of the condensation region with respect to the quiet corona was not more than 15km/s. Discussion of the instrumental profile showed that its effect was small on lines that were much wider than the profile. 相似文献
17.
This paper presents formulas for the calculation of the refraction anomalies caused by the inclination of atmospheric boundary layers. Anomalies were calculated for a few zenith distances for several different atmospheric models. It was established, that near Earth the atmospheric boundary layers have the global inclination in meridian plane near one minute of arc from North to South. They are calculated with standard deviation ±0.2′–±0.35′. The tilts are decreased gradually with the altitude and equal nearly 0 on the heights 8–10 km. Then direction of inclination is changed on opposite (from South to North) and maximum 1′ reaches on the heights 15–18 km. Next inclinations slowly decrease and equal 0 on the heights 28–30 km. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
在此工作中,分析了一个类星体样本的吸收线红移和发射线红移之间的关系。结果表明这两类红移之间存在显著的相关。主要结论:a)反常吸收线红移的主要部分是宇宙学红移;b)吸收体相对于类星体的运动是弱的;c)结果表明产生这些反常吸收线红移的吸收体位于类星体寄主星系或者类星体内部并且朝着类星体运动。 相似文献
19.
The lunisolar perturbation is the principal factor that causes variation in the orbit of a GTO (geosychronous transfer orbit) space debris. In the present article the analytical expression of the long-periodic term of the altitude of the GTO orbital perigee caused by the lunisolar perturbation is derived, and the basic characteristics of the variation of the perigee caused by the lunisolar perturbation are analyzed. A method of selecting a launch window that will help to improve the space debris situation is given, and its correctness is tested and verified through simulation calculation. 相似文献
20.