A stand-alone Program Package for Improvement (PPI) of motion parameters of celestial bodies from observations is described. The PPI is oriented for solving conditional equations system by the method of least squares and is implemented for IBM PC in MS-DOS in the Turbo-Pascal programming language v.5.0. There are two versions of the system:

1. A) using the standard conventional memory 640 Kb and

2. B) using the external memory.

We consider unstable hierarchical triple stars which are disrupted by the straightforward ejection and escape of the distant companion. The main aim of the present work is the study of velocities of escaping stars from these unstable systems, and the dependence of these velocities on the masses of the stars and on the distances of the escapers from the centers of mass of the remaining binary and of the triple system as a whole. Velocities of escapers are estimated for actual star systems. It is shown that in the triple star λ Tau, when it becomes unstable as a result of mass transfer in its close semi-detached binary, the velocity of the escaping distant companion with mass M ≈ 0.7M⊙ can be about 100 km/s. A possible application of these results to the problem of anomalous high-velocity stars in the Galaxy is discussed.

The high angular resolution technique of lunar occultations enables one dimensional source structure in the direction of occultation to be extracted from the observed fringe pattern after detailed analysis taking into account the frequency response of the detection system, the optical filter bandwidth and the telescope size. A program of observing lunar occultations in the near infrared from 1.2m telescope at Gurushikhar, Mt Abu, India (72°47′E, 24°39′N, 1680m), is currently being pursued. Several occultations have been successfully observed in K band (2.2μm) including a day time event. The instrument used was a InSb based infrared high speed photometer, the details of which are given in a earlier paper (Ashok N.M., Chandrasekhar T. and Sam Ragland, 1994, Experimental Astronomy, 4, 177).

The triple star system αCen AB and Proxima Cen - the component C - is the nearest to the Sun. The study of its dynamics has shown that this system is probable non-chance. The motion of the component C (Proxima) with respect to the centre of mass of the pair AB is hyperbolic with the probability P = 1.0. We observe, therefore, a slow passage of C close to the pair AB. We propose the hypothesis that this system is a part of the stellar moving group. We list the probable members of this group amongst the nearby stars. Amongst them we have the binaries Gliese 140.1 and 676, the triple system ADS 10288 (Gliese 649.1), and the six single stars. The probability to find by chance these stars inside the velocity space cube with the side of 20 km/s around αCen is equal to about 2%.

On the basis of numerical simulation of the dynamics of triplets of galaxies, virial estimation of the individual masses of triplets is shown to be unreliable because of their strong nonsteadiness and projection effects: the spread in estimates due to these two factors reaches 2 orders of magnitude. However, the mass of a typical small galaxy group can be estimated statistically, from data on a whole homogeneous ensemble of groups. We propose two different methods of such statistical estimation. Triplets of galaxies offer a good opportunity to measure the amount of dark matter in them, especially because one can use the extensive data set on triplets by Karachentsev et al. (1989). The mass estimates we obtain for the typical group from the Karachentsev's list have more than 5 times excess compared to the visible mass, when a standard mass-to-light ratio is assumed. The typical masses of loose triple galaxies selected from Huchra & Geller (1982) and Maia et al. (1989) catalogues of galaxy groups are also estimated as ≈ 21ML and ≈ 100ML correspondingly. The influence of dark matter distributed in the common envelope on the dynamical properties and the merging rate in small galaxy groups are also considered. It is found that the significant dark matter makes motion of galaxies in groups more stocastic, increases the number of close double approaches between galaxies and increases slightly the merging rate. At the same time, the dark matter significantly decreases the number of long-lived temporary binary subsystems formed inside triplets.

Several modern ground-based optical instruments have indicated similar systematic differences of their catalogues with respect to the FK5. Thus, the FK5 apparently needs a correction of about 60·sin(6δ) mas for northern hemisphere declinations, other sine corrections of order 20 mas and some equator correction. These errors are the result of systematically erroneous proper motions due to position errors, particularly in old observations.

Automated observations of near-Earth asteroids have been underway at the USNO Flagstaff Station since February 1994. Observations are made with an 8-inch transit telescope utilizing a CRAF/Cassini 1024×1024 CCD. The scale of 1.2 arcsec/pixel provides a field 20.5 arcmin on a side. Pointing and imaging are done automatically using nightly schedules of transit times and declinations of the asteroids to be observed. Observations are made in scan mode, allowing an integration time of 80 seconds at the celestial equator and a limiting magnitude of about 17.5. Flats, collimation and scale frames, and photometric standard fields can all be included in the nightly schedules. The telescope operates unattended during the night, but is monitored remotely by observers at another USNO telescope.

We are now at the end of a long symposium which lasted five (but not all full) days. The objective was first to review the best present achievements of astrometry and to present projects for a much more advanced astrometry in terms of precision attained versus the number of stars and limiting magnitudes. The word sub-milliarcsecond astrometry was intentionaly vague. It has rightly been often understood as designating a range of precisions of the order of a few tens microarcseconds.