Space Very Long Baseline Interferometry is an extension of the ground based VLBI to the space. With the launching of two Space VLBI satellites in the future, Space VLBI observations will be available for astrometric, geodetic and geodynamic applications. This new technique holds potential for various important applications including monitoring Earth rotation. The aim of this feasibility study has been to investigate the possibility of precise estimation of Earth rotation parameters from the Space VLBI observations. A simplified mathematical model is derived in terms of estimable parameters. Sensitivity analysis has been carried out to study the sensitivity of this system to the geodetic parameters of interest. Some of the dominant systematic effects have been investigated. Simulation studies have been carried out to study the influence of these systematic effects and a priori information on the estimation of the Earth rotation parameters. The results indicate that the Space VLBI technique may be used to complement other existing techniques for monitoring Earth rotation, only if the orbital systematic effects can be modeled to a high degree of accuracy (or the satellites can be tracked, with high accuracy, independently), and precise a priori information on station coordinates from other sources is used.

A space VLBI satellite is planed to be launched in 1995 by the Institute of Space and Astronautical Science (ISAS), Japan. Together with this satellite, a worldwide collaborative project named the VLBI Space Observatory Program (VSOP) is under developed. Although the project is oriented to imaging mission for compact cores of active galactic nuclei and maser sources, it will open new aspect on all of VLBI applications. The basic design and parameters of VSOP project are reviewed.

For the first time, a new concept of space VLBI's application is presented, in which space VLBI technique is used to sound ionospheric electron content along the ray path.

The VLBI relativistic time delay model of transformation is reformuled with a precision of better than 1 ps, which is given as follows

where is geocentric newtonial potential, and are the barycentric velocity vector in B-frame and the geocentric velocity vector of antenna i. Ŝ is the unit vector of the direction from the barycenter of solar system to the source. c is the speed of light in vacuum. , where is the geocentric baseline vector. δtv can be expressed as in which and

where Δtatm, Δtion and Δtaxo are the tropospheric, the ionospheric and the axio offset refraction delays respectively, and Δtgrav is called the gravitational time delay. A straightforward differentation of expression (1), the equation of d(dτ)/dt can be obtained. The included in the can be expressed as

The orders of magnitude of the various correction terms in expression (4) and (5) are estimated respectively. Conclusion: expression (4) and (5) should be taken into account in the VLBI relativistic model of transformation for the 1 ps precision. Equation (1) and the expression of its differentation differ from all the models which have been published earlier.

The values of the atmospheric time delay for the “Chao”, “Marini” and “CfA−2.2” mapping function are calculated by using the atmospheric parameters in summer and winter at Shanghai, Kunming and Urumqi station respectively. A comparison among these values shows that the derivations of “Marini” from “Chao” and “CfA” are relatively large. On the other hand, the difference of values between the “Chao” and the “CfA” in the case of ∊ = 40° ∼ 10°, which is the average for the three stations, is from +1 mm to +47 mm for the “wet” part of the delay in summer, while is from −2 mm to −28 mm for the “dry” part in winter. For the case of low elevation angle ɛ ≐ 5°, the difference for the “wet” part can be about 400 mm in summer. Therefore, it is indispensable to make a further comparison between “Chao” and “CfA” mapping function by using the data of VLBI observations, in order to make a better revision to the adopted models of atmospheric delay.

The monthly averages of the height of tropopause ht and the tropospheric temperature lapse rate βt for the three stations mentioned above are used to calculate the dry atmospheric delay by the “CfA” mapping function. The results show that the amplitudes of the annual changing of delay dτa, which is caused by ht and βt for the case of ∊ = 20° ∼ 10° at Urumqi station, are about 1 ∼ 5 mm and 2 ∼ 15 mm respectively. Therefore, taking the parameters of ht and βt of the stations into account in “CfA” model, instead of using fixed constants, would be much favourable for the requirements of 1 ps precision of VLBI physical models.

As demonstrated by USNO CCD parallax program, a CCD attached to a modest aperature telescope is capable of measuring stellar trigonometric parallax to a precision better than 1.0 mas. consequently, many objects previously regarded as being too distant for ground-based trigonometric distance determinations can now be considered.

In this paper we show the High-precision parallaxes will provide a very good opportunity for the refinement of H-R digrammes and the calibration of luminosity criteria, we also refer to the open cluster and to determination of accurate stellar masses from close binanies.

The modern astrometric catalogue ACRS invites attempts to re-examine the systematic stellar motions, together with the luni-solar precessional correction and the fictitious equinoctial motion correction to the FK5 system, and gives encouraging results.

On the basis of the three-dimensional Ogorodnikov-Milne model for the overall pattern analysis of the proper motions, the systematic stellar velocity field of about 30000 K-M giants chosen from the ACRS is first examined in the heliocentric distance interval 0.5 to 1.0 kpc. We have found in an iterative fashion a solution for the K-M giants that yields neither deformation-nor vorticity-field other than the classical ones (the Oort constants A and B). The important point to note here is that the generally accepted idea such that the K-M giants are a steady-state constituent of the galaxy is compatible with the luni-solar precessional correction proposed by the VLBI and LLR observations. The K-M giants give the rational set of corrections to the FK5 system: the luni-solar precessional correction Δp = −0″.27 ± 0″.03 / cent and the equinoctial motion correction including the planetary precessional correction Δe + Δλ = −0″.12 ± 0″.03 / cent. Thus, the precessional correction previously proposed with the modern techniques has been confirmed by the pattern analysis of the proper motions.

Next, applying the corrections obtained above, we have performed the overall pattern analysis of the proper motions of about 3000 O-B5 stars, supergiants, and bright giants, which are chosen again from the ACRS, and considered as an entity of the galactic warp. It is found that the kinematics of these stars is quite different from that of K-M giants. These stars show additional shears and rotations around two mutually orthogonal axes lying in the galactic plane, besides the classical ones. The present finding implies that the young stars are streaming around the galactic center in a tilted sheet (the warp) with the velocity of 225 km/s, and the sheet itself is simultaneously rotating around the nodal line of the warp (galactic center — sun — anticenter line) with the angular velocity of 4 km/s/kpc in increasing sense of the present inclination of the warp.

In the framework of the programme of studying the meridional section of the Galaxy (MEGA) the catalogue of stellar data (about 26500 stars) had been compiled and investigated. The main part of the catalogue consist of the proper motions of stars with respect to the galaxies. The stellar kinematical characteristics in the direction of the galactic rotation, the parameters of velocity ellipsoid and the relation between kinematical, spatial and chemical properties of stellar populations have been determined.

Using the proper motions, radial velocities and distances of bright O, B stars taken from the FK5/FK5 suppl. stars, the velocity field of the Gould belt stars has been analysed. The results have been compared with that of the FK4 stars given by Fricke and Tsioumis.

Precessional corrections and stellar kinematic parameters have been derived from the proper motions of 142,171 stars in the updated version of AGK3 (AGK3U). The sky has been divided into 1332 small areas, in which mean proper motions for each component are formed for different magnitude intervals, with and without exclusion of fast stars. Solutions were performed for various kinds of the mean proper motions. Maximum-likelihood algorithm is used to take into account the ellipsoidal distribution of residual velocities. The results for precessional correction are, Δn = 0″.47 ± 0″.03 /cy, Δk = −0″.35 ± 0″.02 /cy, and the results for Oort's constants are, A = 9.5 ± 1.5 km/s/pc, B = −7.5 ± 1.5 km/s/pc.

Using automated scans of Tautenburg Schmidt plates with the APM facility in Cambridge (UK) the mean tangential motion of two globular clusters, M3 and M92, is determined directly with respect to a well defined extragalactic reference frame. In both fields five pairs of plates centred on the cluster with epoch differences from 20 to 27 years were measured. In the independent proper motion determination with 1200 to 2300 reference galaxies for each pair of plates we used 3rd order polynomials and a stepwise regression method. The mean absolute cluster p.m. corrected for systematic effects dependent on the coordinates was obtained with an accuracy of ±0.03 arcsec/century for M3 and ±0.06 arcsec/century for M92.

A programme for the determination of proper motions and photographic B, V, R magnitudes for stars up to 18m within a 4° by 4° region centered near Alcyone is described. We use MAMA measurements of plates taken with Tautenburg and OCA Schmidt telescopes as well as with the double refractor of Bonn and Carte du Ciel plates. To check the stability of the solution three different methods of reduction are applied.

According to the results of the pilot programme a final proper motion accuracy of about 2 mas/a can be achieved for the majority of stars in the survey.

The velocity distribution for the stars of different masses in the typical open cluster was calculated, the velocity variations having been considered as a purely discontinuous random process. the comparison of calculated and observed mean square velocities for the different groups of stars in the Hyades cluster enables us to estimate the mean mass of the stars in the each group.

This Paper investigates population I star samples from the viewpoint of the velocity distributions, each being viewed as a mixture. To obtain information on the class centers, clustering techniques are first applied. Secondly, we use a parametric maximum likelihood formulation that we solve by Redner-Walker's E.M. algorithm. The obtained results are compared and discussed from an astrophysical viewpoint.

The purpose of this paper is to point out the importance of the observation of the counterjet of subluminals, for it will settle up the question whether quasars redshifts are cosmological or not. If so, from the observed wavelength of the counterjet, one is able to find out the value of Hubble constant H0. What we observe as an apparent superluminal or subluminal motion is the resultant velocity of Hubble flow and a local ejection. Taking Hubble flow into account, one can explain problems posed for the relativistic beaming model, such as the one-sidedness problem and the untolerable extension of the deprojected structure of some superluminal sources. Our method is applied to two superluminals, 4C73.18 and 3C179, and two subluminals, M87 and 3C84. Our method can also be applied to investigate the problem of the ejection of the quasar from the galaxy in the framework of kinematics. Two quasar-galaxy pairs, Markarian 205-NGC4319 and 3C455-NGC7413, are studied.

The Permanent GPS Geodetic Array (PGGA) in southern California consists of five continuously operating stations established to monitor crustal deformation in near real time. The near real time requirement has been problematic since GPS satellite ephemerides and predicted earth orientation values (IERS Bulletins A and B) have been found to be neither sufficiently timely nor accurate to achieve horizontal position accuracies of several mm on regional scales. Therefore, we have been estimating precise GPS ephemerides and polar motion since August 1991. An examination of overlapping 24-hour satellite arcs indicates worst-case orbital errors of approximately 0.2 meters in the radial components, 1 meter in the cross-track components and 2–3 meters in the along-track components. A comparison with very long baseline interferometry indicates an accuracy of less than 1 mas in our determination of 24-hour values of pole position. These products are sufficiently timely and accurate to achieve several mm long-term horizontal precision in regional scale measurements of crustal deformation in near real time, as has been demonstrated during the 28 June, 1992 Landers and Big Bear earthquakes in southern California. The PGGA stations were able to detect seismically induced, sub-centimeter-level motions with respect to a terrestrial reference frame defined by the global tracking stations.

A new filtering method, in which the difference of second order is used to filter a time series of equal interval, and an example of its application on the separation of Annual and Chandler wobbles of polar motion are given in the paper.

The short periodical oscillations of variations of Earth rotation parameters (ERP) with periods of about 120, 100, 80, 60, 50 days are the most energetic oscillations after the Chandler and seasonal ones. These oscillations were analysed using SLR and VLBI data and the narrow Ormsby band-pass and Fourier Transformation filters. Polhodes of these oscillations for the last several years were computed. Amplitudes of these oscillations are of the order of 2–5 mas and are changeable. They are modulated with a period of about 600 days.

About 30-year time series of the length of day (LOD) and the Pacific sea level are analysed in the paper. The close correlation between Earth rotation and sea level is discussed. Dynamical analysis of the angular momentum of tropical Pacific Ocean and solid Earth shows that the sea level changes of eastern and western Pacific lead the LOD interannual change in phases of 1 and 2 months respectively. The tropical Pacific effect accounts for about 31% in LOD change and is even more evident during El Nino events. Changes of the Earth rotation also cause changes in the oceanic mass distribution.

The problem on Chandler period is an unsolved one. Several authors suggested a hypothesis that the Chandler wobble is only one free period which slightly changes in time and is amplitude-dependent. In this paper we shall make the hypothesis more rigorous than that has been carried yet. A new deconvolution method for Fourier transform is suggested. Using this method the polar motion data are analysed. The analysis results are shown; the Chandler period is not stable and is indeed amplitude-dependent. The probable explanation for the amplitude-dependent of Chandler period is that, which might be caused by non-equilibrium response of the ocean.