The cosmological constant and the clusters of galaxies

The dependence of the formation redshift of clusters of galaxies on the cosmological constant is discussed on the basis of recent measurements of gravitational masses and radii from X-ray astronomy techniques. For a flat CDM model with several different values of the cosmological constant, the cluster number density as a function of the redshift is calculated. Comparing the calculated number density at z − 0 with the observed value limits the spectrum parameter Γ to the range 0.15–0.32. We also show that if Γ and/or Ω_Λ were larger, many more clusters of galaxies would have been formed at high redshifts.     

大气、陆地水储量和海水质量分布变化与地球低阶引力场球谐系数的关系

大气、固体地球及海洋组成了一个复杂、变化的地球动力学系统，这一系统中的任一质量分布变化都将产生地球引力场变化。采用全球7000多个地面气象台站的月平均降水及温度资料、NCEP提供气压月均值、TOPEX／Poseidon卫星测高资料和WOA98海水温度及盐度模型计算了大气、陆地水储量和海水质量分布变化引起地球低阶引力场系数变化。比较综合大气、陆地水储量和海水质量分布变化对带谐项J2，J3，J4影响的计算结果和人卫激光卫星的测定结果，可以看出，大气、陆地水储量和海水质量分布变化是引起地球低阶引力场系数周年变化的重要激发源。     

Constraints on Jupiters from observations of Galactic bulge microlensing events during 2000

We present observations of eight Galactic bulge microlensing events taken with the 1.0-m Jacobus Kapteyn Telescope (JKT) on La Palma during 2000 June and July. The JKT observing schedule was optimized using a prioritizing algorithm to automatically update the target list. For most of these events we have sampled the light curves at times where no information was available from the OGLE alert team. We assume a point-source point-lens (PSPL) model and perform a maximum likelihood fit to both our data and the OGLE data to constrain the event parameters of the fit. We then refit the data assuming a binary lens and proceed to calculate the probability of detecting planets with mass ratio   q = 10⁻³  . We have seen no clear signatures of planetary deviations on any of the eight events and we quantify constraints on the presence of planetary companions to the lensing stars. For two well-observed events, 2000BUL31 and 2000BUL33, our detection probabilities peak at ∼30 and ∼20 per cent respectively for   q = 10⁻³  and   a ∼ R _E  for a  Δχ²  threshold value of 60.     

Simulating a stochastic background of gravitational waves from neutron star formation at cosmological distances

We develop a temporal simulation of the potentially detectable gravitational wave background from neutron star formation at cosmological distances. By using a recent model for the evolving star formation rate, we investigate the statistical distribution of gravitational wave amplitudes due to supernovae that result in neutron star formation in the Einstein–de Sitter cosmology. We find that the gravitational wave amplitude distribution in our frame is highly skewed, with skewness related to the distribution of sources, and that the potentially detectable gravitational wave strain is dominated by sources at a redshift of     . Time traces of the simulation, using selected waveforms, are presented graphically and are also made available as web-based audio files. The method developed can readily be extended to different cosmologies, as well as to incorporate other waveforms and source types. This type of simulation will be useful in testing and optimizing detection strategies for gravitational wave backgrounds due to various types of individually undetectable astrophysical sources.     

海洋负荷潮汐对地球重力场时变特征影响的理论研究

地球重力场的海潮效应可以看作是一种负荷影响，海潮负荷对重力场的影响在某些台站(例如大洋中的岛屿以及沿海岸地区)可达微伽的量级，因此在高精度的地球重力场的研究中必须加以改正．从理论和方法上研究了海洋负荷潮汐对地球重力场的影响，在推导过程中回避了将点负荷密度展开为球谐函数，而是直接以负荷引力位为基础，并将海潮潮高引入表达式中，推导出了海潮对地球重力场影响的有关公式，同时探讨了在毫微伽精度上需要注意的一些问题．