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Localized astronomical sources like a double stellar system, rotating neutron star, or a massive black hole at the center of the Milky Way emit periodic gravitational waves. For a long time only a far-zone contribution of gravitational fields of the localized sources (plane-wave-front approximation) were a matter of theoretical analysis. We demonstrate how this analysis can be extended to take into account near-zone and intermediate-zone contributions as well. The formalism is used to calculate gravitational-wave corrections to the Shapiro time delay in binary pulsars and low-frequency (LF) pulsar timing noise produced by an ensemble of double stars in our galaxy.c We note that variables r0 and θ0 are not independent and can be expressed through r and θ d Function F (ν) is nomalized to unity, and n(r) = n(θ, r) is normalized to the total number of double stars in the ensemble.

We report observational upper limits on the mass-energy of the cosmological gravitational-wave background, from limits on proper motions of quasars.Gravitational waves with periods longer than the time span of observations produce a simple pattern of apparent proper motions over the sky, composed primarily of second-order transverse vector spherical harmonics. A fit of such harmonics to measured motions yields a 95%-confidence limit on the mass-energy of gravitational waves with frequencies ν < 2 × 10 −9 Hz, of < 0.11h −2 times the closure density of the universe.

Gravitational waves affect the observed direction of light from distant sources. At telescopes, this change in direction appears as periodic variations in the apparent positions of these sources on the sky; that is, as proper motion. A wave of a given phase, traveling in a given direction, produces a characteristic pattern of proper motions over the sky. Comparison of observed proper motions with this pattern serves to test for the presence of gravitational waves. A stochastic background of waves induces apparent proper motions with specific statistical properties, and so, may also be sought. In this paper we consider the effects of a cosmological background of gravitational radiation on astrometric observations. We derive an equation for the time delay measured by two antennae observing the same source in an Einstein-de Sitter spacetime containing gravitational radiation. We also show how to obtain similar expressions for curved Friedmann-Robertson-Walker spacetimes.Comment: 31 pages plus 3 separate figures, plain TeX, submitted to Ap

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Changes in the circulation of the earth's atmosphere cause fluctuations in the length of day (LOD) by exchanging angular momentum with the surface of the earth. In this paper we examine the earth's polar angular momentum budget using earth rotation data from optical astrometry and lunar laser ranging together with simultaneous estimates of the atmospheric angular momentum Matm derived from meteorological data. The atmospheric excitation can explain most of the observed LOD fluctuations at periods between 700 and 40 days. The observed Matm spectral power is proportional to the inverse frequency squared for periods between 1 year and 3 days and flattens out at higher frequencies. The LOD and Matm spectra are very similar except at periods of <40 days, where the LOD measurement noise dominates. The Matm ‐ LOD coherence is highly significant between periods of 700 and 40 days. There is no evidence for phase shifts between the Matm and LOD data at periods between 600 and 40 days. A broad peak is clearly evident at periods of 40–60 days in the spectra of all three time series. The LOD data have a long‐term drift, not matched by the Matm data, that is probably the result of a core‐mantle angular momentum exchange. There are significant imbalances in the angular momentum budget. Most of the seasonal imbalance can be attributed to the effects of systematic errors in the meteorological data, but some of this discrepancy may be caused by exchanges of angular momentum with the oceans. The semiannual, monthly, and fortnightly tidal variations in the earth rotation were detected, and the observed amplitudes of these variations are consistent with theoretical estimates.