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G. B. Hobbs R. T. Edwards R. N. Manchester 《Monthly notices of the Royal Astronomical Society》2006,369(2):655-672
Contemporary pulsar-timing experiments have reached a sensitivity level where systematic errors introduced by existing analysis procedures are limiting the achievable science. We have developed tempo2 , a new pulsar-timing package that contains propagation and other relevant effects implemented at the 1-ns level of precision (a factor of ∼100 more precise than previously obtainable). In contrast with earlier timing packages, tempo2 is compliant with the general relativistic framework of the IAU 1991 and 2000 resolutions and hence uses the International Celestial Reference System, Barycentric Coordinate Time and up-to-date precession, nutation and polar motion models. tempo2 provides a generic and extensible set of tools to aid in the analysis and visualization of pulsar-timing data. We provide an overview of the timing model, its accuracy and differences relative to earlier work. We also present a new scheme for predictive use of the timing model that removes existing processing artefacts by properly modelling the frequency dependence of pulse phase. 相似文献
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From the analysis of all available radiometric measurements of distances between the Earth and the major planets (including
observations of martian landers and orbiters over 1971–2003 with the errors of few meters) the positive secular trend in the
Astronomical Unit AU is estimated as
. The given uncertainty is the 10 times enlarged formal error of the least-squares estimate and so accounts for possible
systematic errors of measurements and deficiencies of the mathematical model. The reliability of this estimate as well as
its physical meaning are discussed. A priori most plausible attribution of this effect to the cosmological expansion of the
Universe turns out inadequate. A model of the observables developed in the frame of the relativistic background metric of
the uniform isotropic Universe shows that the corresponding dynamical perturbations in the major planet motions are completely
canceled out by the Einstein effect of dependence of the rate of the observer’s clock (that keeps the proper time) on the
gravitational field, though separately values of these two effects are quite large and attainable with the accuracy achieved.
Another tentative source of the secular rate of AU is the loss of the solar mass due to the solar wind and electromagnetic
radiation but it amounts in
only to 0.3 m/cy. Excluding other explanations that seem exotic (such as secular decrease of the gravitational constant)
at present there is no satisfactory explanation of the detected secular increase of AU, at least in the frame of the considered
uniform models of the Universe. 相似文献
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New physics beyond the standard model of particles might cause deviation from the inverse-square law of gravity. In many theoretical models of modified gravity, it is parameterized by the Yukawa correction to the Newtonian gravitational force in terms of two parameters α and λ. Here α is a dimensionless strength parameter and A is a length scale. Using the supplementary advances in perihelia provided by INPOP10a and EPM2011 ephemerides, we obtain new upper limits on the deviation from the inverse-square law when the uncertainty of the Sun's quadrupole moment is taken into account. We find that INPOP10a yields the upper limits as α =- 3.1× 10-11 and λ= 0.15 au, and EPM2011 gives α = 5.2 × 10-11 and λ=- 0.21 au. In both of them, α is at least 10 times less than the previous results. 相似文献
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数值积分方法是进行天体力学研究的重要工具, 尤其对于行星历表的研究工作而言. 由于在使用数值方法计算天体轨道时, 最终误差通常是难以预知的, 所以在面对精度要求较高或者积分时间较长的工作时具体积分方案的设计---尤其是当使用定步长方法时的步长选择---需要十分谨慎, 因为这将意味着是否能在时间成本可以被接受的范围内使解的精度达到要求. 因此, 在使用数值方法解决实际问题时如何快速寻找效率与精度之间的最佳平衡点是每一个数值积分方法的设计者与使用者都会面临的难题. 为解决这一问题, 在定步长条件下对数值积分方法的舍入误差概率分布函数以及截断误差积累量对步长的依赖关系和随时间的增长关系进行了深入研究. 基于所得结论, 提出了一种仅需较少的数值实验资料即可对选择任意时间步长积分至任意积分时刻时的舍入误差概率分布函数与截断误差积累量进行准确估计的方法, 并使用Adams-Cowell方法对该误差估计方法在圆周期轨道条件下进行了验证. 该误差估计方法在未来有望用于不同数值算法的性能对比研究, 同时也可以对数值积分方法求解实际轨道问题时的决策工作带来重要帮助. 相似文献
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Proposals for the masses of the three largest asteroids,the Moon-Earth mass ratio and the Astronomical Unit 总被引:1,自引:0,他引:1
We propose to the NSFA (the IAU Working Group on Numerical Standards for Fundamental Astronomy) the following representative
values and realistic uncertainties for the masses of the three largest asteroids (Ceres, Pallas, Vesta), to be used as the
current best estimates:
Unlike the values previously adopted in the Astronomical Almanac, these are consistent with nearly all of the twenty or so
modern accurate determinations from various authors. We also have proposed the following values for the Moon-Earth mass ratio
and the astronomical unit in meters obtained from the ephemeris improvement processes at JPL in Pasadena and at IAA RAS in
St.Petersburg: M
Moon/M
Earth = 0.0123000371(4) and AU = 149597870700(3) m. The numerical value of the AU in meters is identical in both the TDB-based and the TCB-based systems of units if one uses the conversion proposed by Irwin
and Fukushima, Brumberg and Groten, Brumberg and Simon. 相似文献
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S. E. Shaw A. B. Hill E. Kuulkers S. Brandt J. Chenevez P. Kretschmar 《Monthly notices of the Royal Astronomical Society》2009,393(2):419-428
The timing properties of the 4.45 s pulsar in the Be X-ray binary system GRO J1750−27 are examined using hard X-ray data from INTEGRAL and Swift during a type II outburst observed during 2008. The orbital parameters of the system are measured and agree well with those found during the last known outburst of the system in 1995. Correcting the effects of the Doppler shifting of the period, due to the orbital motion of the pulsar, leads to the detection of an intrinsic spin-up that is well described by a simple model including and terms of −7.5 × 10−10 s s−1 and 1 × 10−16 s s−2 , respectively. The model is then used to compare the time-resolved variation of the X-ray flux and intrinsic spin-up against the accretion torque model of Ghosh & Lamb; this finds that GRO J1750−27 is likely located 12–22 kpc distant and that the surface magnetic field of the neutron star is ∼2 × 1012 G. The shape of the pulse and the pulsed fraction shows different behaviour above and below 20 keV, indicating that the observed pulsations are the convolution of many complex components. 相似文献
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Until recently, the Global Positioning System (GPS) was the only operational means of distributing time to an arbitrary number
of users and of synchronizing clocks over large distances with a high degree of precision and accuracy. Over the last few
years it has been shown that similar performance can be achieved using the Russian Global Navigation Satellite System (GLONASS).
GLONASS time transfer between continents was initially hampered by the lack of post-processed precise ephemerides. Results
from the International GLONASS Experiment (IGEX) campaign are now available, however, and this paper reports on the first
use of IGEX precise ephemerides for GLONASS P-code intercontinental time links. The results of GLONASS P-code and GPS C/A-code
time transfer are compared under similar conditions.
Received: 31 January 2000 / Accepted: 10 July 2000 相似文献