We present a concept for a scanning interferometer for global (wide-angle) astrometry from space. The GAIA concept has been proposed for the European Space Agency's long-term scientific programme. It consists of three Fizeau-type interferometers with 2.5 m baselines, set at large and fixed angles to each other. Complete utilization of the instrument's resolution and sensitivity requires a new type of photon-counting detector, combining very high spatial and temporal resolution. An array of superconducting tunnel junctions (STJ) may ultimately provide this capability. Pending this development we describe a focal-plane configuration for GAIA using existing technology in the form of a modulating grid and CCD detectors. We estimate that 50 million stars brighter than V = 15.5 could be observed on the 10 to 20 microarcsec accuracy level. In addition, high-precision multi-colour, multi-epoch photometry is obtained for all objects.

Optical interferometry is ensconced as an ‘area of future interest’ (a socalled Green Dream) in Horizon 2000, the long-term scientific plan of ESA. Over the years, there have been three large ESA workshops on Space interferometry, where many different concepts and designs were proposed, and several ESA committees have studied the possibilities. These committees were also involved, in an advisory role, in a modest technological research program (TRP) by ESTEC. In 1990, the Space Interferometry Study Team (SIST) recommended building an optical interferometer, consisting of 10-15 small telescopes attached to an 100m inflatable structure, as a scientifically interesting first step. The SIST even produced a workable design. It quickly became clear, however, that such an undertaking would cost much more than an ESA cornerstone mission, and was thus far too ambitious. Simultaneously, another ESA study team (LIST) came to the conclusion that the Moon, contrary to earlier beliefs, does not offer a particularly suitable environment for interferometry. At the Beaulieu workshop in 1992, it was decided to try to achieve cornerstone status for one or two smaller interferometry missions in Space: a 10m UV imaging interferometer, or an interferometric successor to the astrometry satellite Hipparchos. The latter seems to have a good chance at the moment, in the form of the GAIA proposal which has been selected for further study for the new ‘post-Horizon 2000’ program. GAIA may have some limited imaging capability, but a true imaging interferometer in Space will have to wait for a few decades yet.

The Moon is generally considered to be an ideal site for astronomy, offering excellent observing conditions and access to the entire electromagnetic and particle spectrum. A wide range of astronomical observations can be carried out from the Moon, but, as concluded in a recent ESA study (Mission to the Moon 1992), only a restricted number could be better implemented from a lunar site rather than from any other location. Very low frequency (VLF) astronomy, astrometry and interferometry fall into this category, as well as a transit telescope to map dark matter in the Universe. Whilst VLF and astrometric telescopes should be automatic, long baseline interferometers will probably require human intervention and will thus benefit from a manned lunar base.

At Kyiv University Observatory, in accordance with IAU resolution, the Combined Catalogue of Positions and Proper Motions of 5115 Bright Stars in the FK5 system for Epoch and Equinox J2000.0 (BSC, see reference) has been compiled using 20 source catalogues obtained within the framework of ‘Bright Stars’ International Program. The source catalogs are Bordeaux-66, Bucharest-65, Bucharest-68, Belgrade-79, Cape-68, Kharkiv-70n, Kharkiv-70s, Kyiv-66, Kyiv-73, El Leoncito-70, Moscow-76, Mykolaiv-65, Perth-70, Perth-75, Santiago-65, Santiago-67, Strasbourg-65, Tashkent-64, Tokyo-68, Washington-66. The BSC accumulates around 30,000 source catalogue positions observed within 1960-1980. The standard errors of BSC do not exceed 0.1 arcsec and 0.25 arcsec/cy for positions and proper motions, respectively. The systematic differences between BSC and FK5 in positions for the mean BSC epoch 1970 as a rule do not exceed several hundredths of arcsec. A comparison of the BSC with the PPM catalogue indicates that in the latter the accuracy of positions and proper motions of the ordinary bright stars is slightly worse than that of average values given by the authors of the PPM. It is important to note that the comparison of the BSC with PPM for various star subsets shows deviations of both the HPS bright star system and the rest of the PPM bright stars, on the one hand, from the stars of the FK5 Extension contained in the PPM on the other hand. To examine the BSC proper motion system the stellar astronomy constants and correction to precession have been determined using the BSC proper motions. The parameters obtained agree with the standard ones. But the Oort constants are slightly smaller than those of standard.

The BSC catalogue as a whole is acceptable for astrometry usage with respect to both accidental and systematic accuracy.

There exist no special astrometric telescopes or devices suited to determine precise positions, proper motions and parallaxes in the infrared. Only astrophysical IR observations are carried out now in the range of 1-350 μm. But many astronomical problems concerning galactic structure and kinematics and others may be solved if astrometric instruments and methods are developed and implemented for IR observations. Development of new technology and infrared array receivers gives the hope that many astrometric problems in the infrared would be solved successfully.

Pulkovo and Valencia observatories are developing measuring machines based on the “Ascorecord” microscope that allow to undertake automatic measuring programs of different kind of plates (Ortiz et al., 1993). All aspects of astrometry work are covered now by our software: field maps and plate files creation from the PPM and the GSC; precise ephemeris calculation of minor planets and comets, including planetary perturbations; image identification and automatic plate measurement and reduction (Lopez et al., 1994a). For these tasks, correction tables for GSC catalogue vs. PPM, systematic errors (Lopez et al., 1994b) have been obtained. Observing programs using plates and CCD devices at telescope focus are planned (the search of new asteroids and comets, big planets satellites observation, new high density photographic catalogues and some other projects).

Six observatories of the former USSR carry out photographic observations within the FON project (the fourfold coverage of the northern sky) since 1982. The same type wide-angle Zeiss astrographs (D=400 mm, F=2000 and 3000 mm) are used. At present Golosiiv Observatory almost finished the Kiev observational part of the project and the measurements of onefold coverage plates have been started. The special measuring machine PARSEC (Programming Automatic Radial-Scanning Coordinatometer) has recently been constructed for this purpose.

We intend to apply the measurements of the FON project plates to the determination of new positions and proper motions of all stars in the Astrographic Catalogue (AC) using the last one as the first epoch of observations. AC is applied also as input catalogue for PARSEC. About 500 plates have been measured at the moment and proper motions for more than 500000 stars in different areas of the northern sky have been obtained.

The accuracy of the FON positions and proper motions of stars from the measurements of onefold coverage plates is estimated to be 0.35 arcsec and 0.006 arcsec/yr, respectively.

Futher investigations will be carried out in cooperation with Sternberg Astronomical Institute (Moscow, Russia) and Astronomisches Rechen-Institut (Heidelberg, Germany).

The above-described reasearches became possible partly by Grant N V41000 from the International Science Foundation.

We present the status of the Yale/San Juan Southern Proper Motion program (SPM) which is the southern hemisphere extension of the Lick Observatory Northern Proper Motion program with respect to faint galaxies (Platais et al., 1993). To date, measurements and reductions in the South Galactic Pole region comprising ≈ 1000 square-degrees on the sky have been finished. At this stage of the SPM program particular attention has been paid to the plate model choice along with an assessment of and accounting for systematic errors. For our establishing of a secondary reference frame we have noticed the presence of a potentially dangerous effect, so–called field–independent coma which is caused by lens decentering. We acknowledge the superb Hipparcos preliminary positions without which such analysis would be virtually impossible. The SPM data at the SGP region have also been used to constrain a multi–component Galaxy model. First results of this analysis are presented.

The Bordeaux automatic meridian circle has been working for 10 years with a tracking photoelectric micrometer. This micrometer was recently replaced by a focal CCD camera in order to extend the differential position measurements to much fainter stars with improved accuracy.

The star Gliese 623 (RA = 16h 22.6m; Deal = +48°28′ [1950]), π = 0.″138; mv = 10.3; Sp dM3, (Woolley et al., 1970)) is observed at Pulkovo by means of the 26-inch Refractor. The series of 95 plates (about 600 individual positions) obtained during 1979–1994 has been studied. This set has shown perturbations in the motion of this star under the influence of a dark component which has been investigated earlier by different methods (see, for instance, Marcy & Moore, 1989). The following values of relative proper motion and parallax with their mean errors and preliminary elements of the photocentric orbit have been adopted on the base of our observations: μx = +1.″1483 ± 0.″0010; μy = −0.″4462 ± 0.″0009; πx = 0.″126 ± 0.″019; πy = 0.″136 ± 0.″017; P = 3.76 years; e = 0.50; To = 1984.28. With the use of modified Thiele – Innes constants the following elements of the orbit have been determined: α = 0.″052 ± 0.″006 (m.e.) and i = 141°; ω = 265°; ω = 126°. We may suppose that the lower limit of the mass of the component is about 0.09 masses of the Sun. Our study has shown small periodic deviations in the distances between the components of δ Gem and ADS 11632, which may be evoked by substellar and stellar companions of low masses (Shakht, 1988).

A 1.5 m reflector is proposed for infrared and optical meridian observations in order to extend the fundamental coordinate system to faintest objects and to the K-infrared waveband. Classical meridian circles are unfit for the infrared observations because their lens objectives do not give good images in the infrared. But reflectors are almost never used as meridian circles due to uncertainties in their optical axis position. The main problem is that the secondary mirror is not connected with the micrometer and the circle reading system. In order to overcome this difficulty the author proposes to use an intermediary focal plane between the primary and the secondary mirrors where a luminous reference grid of wires might be placed. The Gregory optical scheme has such a focal plane, and its secondary mirror forms images of a star and the grid at the micrometer's detecting area. At the same time a special champher around the primary's central hole forms anautocollimated image of the grid near the grid itself. The micrometer measures the star image coordinates relative to two images of the reference grid. So, observations will not be affected by displacements of the secondary mirror and by those of the micrometer. The telescope's equivalent focal length has been chosen as 3 m, and the optical system has been transformed into an aplanatic Mersenne combined with an aplanatic focal reducer corrector (Popov, 1988). A new autocollimated circle reading system is chosen for the instrument (Yershov and Nemiro, 1994). The observations will be linked to the fixed optical axis of two long-focus collimators placed at the prime vertical plane.

A new autocollimation circle reading system is proposed for the reflector meridian circle (Nemiro and Streletsky, 1988). The instrument will be used for observations in the K-infrared waveband. Instead of the divided circle fixed to the instrument tube the new system has small spherical mirrors polished at the lateral surfaces of the primary mirror. The primary mirror is made from sitall and has an autocollimation system aimed at monitoring its optical axis position. The small spherical mirrors of the circle reading system link the circle readings with the primary's optical axis. The divided circles are fixed unmovable opposite to both lateral surfaces of the primary's optical block. Both surfaces have four spherical mirrors. The distance between the divided circles and the mirrors is equal to the mirrors' radii of curvature. The scales of each circle are illuminated from outside (where the measuring microscopes are placed). The mirrors form autocollimated images of the divisions at the plane of the divisions itself. Averaged coordinates of a division and its autocollimated image give the position of the mirror's optical center, and the semi-difference of the coordinates gives the angular position of the telescope. So, the measurements of the circle positions are differential ones, and any displacements of the microscope zero-points are not critical. The precision of measurements is estimated to be better then 0.05″ (random) and 0.005″ (systematical). The work was supported by the Russian Foundation of Fundamental Investigations (the project's code is 93-02-17095).

Long baseline optical interferometry has been successfully employed to measure the diameters of stars. In this technique, bandwidth smearing can affect the measurement accuracy. These bandwidth smearing effects can be, to some extent, eliminated by dividing the whole observing spectral band into sub-bands and calculating the star's diameter based on the visibilities and spatial frequencies at the corresponding sub-bands. In the visible range, dividing the whole spectral band can be implemented by introducing a spectrograph, while in the IR domain, this operation can be performed efficiently with the technique of double Fourier interferometry (DFI) without losing the advantage of multiplexing. In particular, the use of IR single-mode fiber optics for DFI will make the interferometer extremely compact, light, insensitive to surrounding conditions, etc. We established an IR single-mode fiber optic double Fourier interferometer in the laboratory, in which the optical path difference modulations are generated by stretching fiber arms and the beam combination is carried out with a fiber optic directional coupler. In this paper, we report on experiments and experimental results from measurements of the diameter of an artificial star with the technique of fiber optic DFI.

The location method and accuracy analysis has become a very important subject in astrometry since the photoelectric technique was widely applied. The location methods of the stellar images observed with the slit micrometer are discussed in this paper, and a new estimation method called the maximum correlation procedure is presented. This procedure has already been used to process and analyze the observational data. Because of the ideal mathematical performance of the correlation function, the procedure provides us a good way to determine image locations. By means of simulated observations according to the theoretical analysis, we find that the locating accuracy and the limiting magnitude for this method is much higher than those of traditional locating method. For the observational data of about one thousand stars obtained with the Photoelectric Astrolabe at Yunnan Astronomical Observatory, the positional accuracy of a single star using the maximum correlation is improved by 0.045 arcsec over that with the median. The maximum correlation procedure has also increased the data reduction ability for faint star observations with very low signal to noise ratios.

The main complication to use CCDs for astrometry is their small linear size. Nevertheless, a wide range of traditional astrometric problems can be solved by use of short-focus astrographs equipped with available CCDs. They are: creation of large astrometric and photometric catalogues, link of optical catalogues to an extragalactic reference frame, observations of the solar system bodies, etc. It can be shown that a telescope with focal length of 1-2 meters, equipped with a single CCD can produce a huge amount of simultaneous positional and photometric observations of high precision. It will be especially effective when the Tycho catalogue will be completed, because the problem of precise reference system in a small field of view (about 1 square degree) will be solved with extremely high accuracy. The majority of stars up to 18-20 magnitude can be observed with such an instrument. The problem of resolving “close” stars arises only for some very dense areas on the sky, such as globular clusters etc. – The results of CCD-observations made at Pulkovo with a small short-focus astrograph (D=100 mm, F=712 mm, FOV=45 × 67 arcmin) in 1993-1994 show that the precision of single observation is not worse than: in right ascension −0.15 to 0.35 arcsec, in declination — 0.10 to 0.25 arcsec (the size of pixel was 18 × 24 μm2), and in magnitude — 0.05 to 0.15 mag in a wide range of magnitudes from the brightest objects to V=16. From a series of 5–10 frames it is possible to obtain positions and magnitudes of a large number (up to 500–600 in one frame) of stars with a precision quite comparable with that of normal astrographs and other “large” telescopes.

The Mykolayiv axial meridian circle (AMC) consists of a horisontal telescope with a pentagon prism of ‘CITALL’ in front of the objective of D=180mm and F=2480mm in the meridian, and a fixed aligned vacuum collimator of D=180mm and F=12360mm.

Investigations of the AMC parameters show that: horizontal flexure is negligible and about −0.037″; collimation is stable and can be described by the formula C = C′ + a · t, where t[C] is the temperature, a = 0.026″ and C′ const. The variation of collimator inclination is of the order 0.09″ per 1°C Test observations of FK5 stars show variations of the AMC intrumental system of not more than 0.1″.

A CCD micrometer is being developed. Test observations with a pilot micrometer with a CCD of 288 × 256 pixels have started. It appears that the AMC magnitude limit (with cooling) will be about 14 and the positional accuracy 0.1 arcsec.

Finally, the expected capabilities of the fully automatic Mykolayiv AMC permit its efficient use for extention of the stellar reference frame to fainter magnitudes, for linking the optical/radio reference frames. In particular, for future observations a programme of 12–14m reference stars around extragalactic radio sources is being prepared.

An ideal receiver of radiation should record the arrival time and coordinates of each incoming photon. Available CCD arrays (accumulation mode) and microchannel plate detectors (photon counting mode) are mere approximations to the ideal configuration.

A portable computer program called SUBPLATE was developed to implement the sub-plate overlap technique proposed by Taff (1989 AJ 358, 359). The main point of the technique is to divide the plate into smaller pieces and then to overlap them, each with a minimum number of reference stars to solve for a linear solution.

We have been doing a sample survey in UBV photometry and proper motions as part of an investigation of galactic structure and evolution. The 3 fields in the direction of galactic anticentre (l = 167°, b = 47°), centre (l = 3°, b = 47°) and antirotation (l = 278°, b = 47°) have been surveyed. The high astrometric quality of the MAMA machine (CAI, Paris) gives access to micronic accuracy (leading to < 2 mas per year) on proper motions with a 35 years time base. The kinematical distribution of F and G–type stars have been probed to distances up to 2.5 kpc above the galactic plane. We have derived the constrain on the structural parameters of the thin and thick disk components of the Galaxy (Ojha et al. 1994abc):

• • The scale lengths of the thin and thick disks are found to be 2.6±0.1 and 3.3±0.5 kpc, respectively. The density laws for stars with 3.5≤MV≤5 as a function of distance above the plane follow a single exponential with scale height of ∼ 260 pc (thin disk) and a second exponential with scale height of ∼ 800 pc (thick disk) with a local normalization of 5–6% of the disk.

• • The thin disk population was found with (〈 U+W〉, 〈V〉) = (1±4, −14±2) km/s and velocity dispersions (σU+W, σV) = (35±2, 30±1) km/s. The thick disk population was found to have a rotational velocity of Vrot = 177 km/s and velocity dispersions (σU, σV, σW) = (67,51,42) km/s. No dependence with r and z distances was found in the asymmetric drift measurements of the thick disk population.

We explore the proper motion distributions of anisotropic Plummer models, and show that accurate measurements on the proper motions and radial velocity of individual stars can lead to information on the distance of a stellar system. We consider a one-parameter family of models, which all have the same Plummer law in the mass density, but have different anisotropic 2-integral distribution functions F(E, L), and hence different orbital structure (Dejonghe 1986). The input data for M13 are the photometry and the radial velocities as measured by Lupton, Gunn & Griffin (1987, AJ, 91, 1114), and the proper motion data as measured by Cudworth (1979, AJ, 84, 774). We represent the distribution function as a power series expansion in Fricke-type form. The Quadratic Programming (QP)-algorithm (Dejonghe 1989, Ap.J., 343, 113) determines the coefficients in the expansion by minimising a χ2-type variable, subject to the constraints that the distribution function must be positive in phase space. From the photometry we calculate the spatial mass density (the well-known Abel inversion) and the potential. The total mass is accounted for by applying a suitable scaling on the kinematical data. All models have a constant M/L. We use surface luminosities and the 3 (anisotropic) pressures, which depend on the three velocity dispersions. By re-iterating the procedure for various distances (and masses), the best distance estimate can be obtained.