For the past 30 years purposeful, highly accurate photographic observations have been carried on in Abastumani to solve a series of astrometric problems. The principal observational instruments are a 70 cm Maksutov system mirror telescope — AS-32 (F = 2100 mm) and a 40 cm double Zeiss astrograph (F = 3000 mm).

A measuring accuracy of about 0.3 μm per coordinate for well exposed stellar images is achieved over the entire usable measuring area of more than 200 × 200 mm2 with the CCD-camera upgrade of the ‘old’ Mann comparator.

The external plate-to-plate comparison shows that the error due to emulsion shifts dominates, which results in an overall accuracy of about 0.8 μm.

While digitizing the first 1500 photographic plates (astrograph plates and prime focus plates of various telescopes) using our CCD-based measuring machine, we gained a detailed understanding of the properties of the digitized stellar images. These images are different from those obtained by digitizing photographic plates with microdensitometers and similar scanners. Therefore it was necessary to reject the modelling methods given in the literature and compose new models that describe the stellar images more accurately.

First results of simulating the whole imaging process, starting with the atmosphere, aberrations of the telescope, etc., and ending by including the imaging-properties of our measuring machine, show good agreement with the measured images as well as the modelling functions.

The number of known double stars is steadily increasing, thanks to ground-based and space observations. Therefore the ratio of known double to single stars has to be revised upwards continuously. With the Hipparcos parallaxes it will be possible to get stellar statistics for precisely defined volumes of space. This will lead to strong constraints on all astrophysical calibrations of masses, spectral types and luminosities in the solar neighbourhood. A European network of laboratories was created in August 1990 in order to remedy the lack of photometric data for close visual double stars. This network intends to study all aspects of formation and evolution of double and multiple star systems. The immediate goal of the group is to provide the scientific community with a compilation of known photometric data on a large selection of close visual double stars and to significantly enlarge this information by new observations with modern devices. A photometric database of stellar systems is being compiled from most widely used photometric systems in collaboration with the ‘Centre de Données Stellaires’ of Strasbourg.

The machine measurements of UK Schmidt plates have produced two very large galaxy surveys, the APM survey and the Edinburgh-Durham Southern Galaxy Catalogue (or COSMOS survey). These surveys can constrain the power on large scales of ≳ 10h−1 Mpc better than current redshift surveys, simply because such large numbers, ≳ 2 million galaxies to bJ ≤ 20.5, provide very high signal/noise in the estimated two-point correlation function for galaxies. Furthermore, the results for the three-dimensional galaxy two point correlation function, ξ(r), obtained from the measured projected function, ω(θ), should be quite robust for reasonable model number-redshift distributions, N(z), for these magnitude limits (see, e.g., Roche et al. 1993). Another clear advantage of measuring ω(θ) is that it is unaffected by the peculiar velocities of the galaxies, whereas they have an important effect on the corresponding ξ,(s) using galaxy redshift surveys.

Accurate astrometric and photometric calibrations of all-sky photographic surveys, such as the Palomar Quick-V survey and the UK SERC-J survey, digitised for the construction of the Hubble Space Telescope Guide Star Catalog, are of extreme astrophysical value. Their wide range of applications includes, for example, galactic structure, stellar populations, extragalactic studies, and deep sky catalogs for mission planning and telescope operations. The Guide Star Photometric Catalog (GSPC-I, Lasker et al. 1988) provides stellar calibration sequences, placed approximately in the center of each survey plate, with a limiting magnitude of V = 15 mag. The goal of our program is to extend these calibrators to V = 20 mag in the Johnson-Kron-Cousins B, V and R passbands, with an accuracy of 0.05 mag. This is accomplished by taking CCD frames centered on the faintest star of each GSPC-I sequence. Typically, both long and short exposures are acquired in each field in order to link the bright and faint ends of the sequence.

A wide-field CCD has been used to obtain photometry of resolved stars in the main body of the Local Group Dwarf Irregular Galaxy NGC 6822. Under good seeing conditions, the relatively large pixel size of the chip produces a poor sampling of the stellar profiles. This paper discusses how this undersampling affects the quality of the photometry and shows that this problem can be overcome when the point-spread function is suitably modelled. Finally, a brief discussion of the stellar content of NGC 6822 is given in the light of the [(V-R), V] colour-magnitude diagram.

On photographic plates taken for the purposes of classical stellar photometry (using a standard stellar sequence) there usually is no external photometrical calibration scale, neither a wedge nor spots; and hence the transition to relative intensity is a problem. The construction of a characteristic curve D(I) (hereafter CHC) by combining density profiles of several standard stars is a perfect solution of this task (Agnelli et al. 1979; de Vaucouleurs 1984). We have developed this method in order to obtain internal photometric calibrations for a large number of plates taken at the RC focus of the 2m telescope (F/8, scale 12.86) at the National Astronomical Observatory (NAO); these do not have any photometrical calibration. Our long term project provides UBV stellar photometry in the central regions of some globular clusters — M5, M10, M12, M56, M71, for which we have good collections of short exposure plates. The task also requires a background determination which can be done precisely only in relative intensities. We apply the method using Arp's UBV standard sequence in M5 globular cluster. In our investigation we demonstrate some peculiarities of the method:

Usually, the reduction of iris-measurements d of stellar photographic images to magnitudes m is performed with one-dimensional regression m = f(d), obtained using standard stars (Burkhead & Seeds 1971). The derivation of accurate magnitudes is difficult due to many factors (Butler 1972). Considering that the star image shape contains information on the sensitivity of the plate and the color of the star, Vladimirov (1978) recommended multi-parametric determination of the magnitudes, using a system of isodense bounded areas of the stellar images. Here this approach is implemented using software that performs a general multi-parametric method (MPM) of iris-photometry.

Surface photometry techniques of data processing are applied for the qualitative analysis on the reflectivity of the two mirror system in the prime focus of the 2m Ritchey-Chrétien Coudé telescope of the Rozhen Observatory. There are considerable variations in the reflectivity, up to ±30%. An estimation on the upper limit of the average reflectivity, about 68% ±1%, of the two-mirror RC system is made. A loss of about 0.5 magnitudes in the limiting magnitude due to the low reflectivity and to the decrease in the reflecting surface is found.

Conversion of light detector signals to intensity values is one of the most important factors influencing precision of spectroscopic observations. Most of the classical light detectors used in astronomical practice are more or less nonlinear. As the photoemulsion has long been the most widespread nonlinear light detector, many improvements in the calibration methods concerned its nonlinearity. In addition to it, there are other substantial sources of inaccuracy in the calibration process of real astronomical images and spectrograms. They are mostly related to real light conditions in telescopes and spectrographs, as well as to the wavelength dependent sensitivity of light detectors. Some of these factors can be taken into account and involved in the calibration process. Similar effects are considered when a flat-field is evaluated for CCD detectors or when image structure varies over a photographic plate.

Currently, IIIa-J objective-prism plates from the Calar Alto and ESO Schmidt telescopes are used at the Hamburg Observatory to search for and to identify new astronomical objects. Major projects are the Hamburg Quasar Survey, the Hamburg-ESO Survey, and the Hamburg-Munich collaboration to identify sources from the ROSAT All-Sky Survey (cf. contributions to this conference by Hagen et al., Wisotzki, and Voges). The objective-prism plates are digitized with a PDS microphotometer. To determine the brightness of the digitized objects, a method to calibrate the plates was developed, using an internally determined characteristic curve and its external calibration with photometric sequences. Having spectral information, we are able to synthesize the Johnson B-filter as this filter is fully covered by the spectra.

Several digital techniques have been used to remove large-scale background variations caused by manufacturing and technology of the photographic processing on old photographic plates ORWO ZU-21. Suppression of these large-scale background variations improved the study of large-scale phenomena in cometary plasma tails and the determination of the solar wind characteristics.

The results obtained from five images of the comet Bradfield 1987 XXIX have been compared. It has been shown that the simple digital techniques used were applicable also to photographic plates with images of lesser quality. They may be utilized in the treatment of old photographic plate archives.

The function of astronomers is to capture and create information and send it into the future. The vehicle for this transmission of knowledge is the archive. The digital revolution is quickly rendering our paper and glass archives obsolete; great challenges exist in creating archive systems for digital data. We can only meet these challenges by substantial shared effort.

Modern astronomical data is now either produced directly in digital form or converted from a high resolution analog medium to digital form. These data are therefore best conserved and handled with computer techniques.

This paper will first define ‘computer storage technology’ as the set of software and hardware tools needed to perform the management of an archive and the control of the archiving and redistribution operations. Various implementation choices that one faces when setting up an archive will be reviewed. The chasm between the life expectancy of the stored data and that of the equipment and procedures needed to handle it will be one of the most important points considered.

Currently available technological solutions will be reviewed. Future trends of the storage technology will be discussed in comparison with the expected data production rate of the next generation astronomical instruments.

Any astronomer, whether preparing observation runs or reducing data, requires access to information concerning the objects under investigation. Ideally the data should be from several wavelengths and should be as quantitative as possible. This leads to the concept of developing simultaneous interactive access to sky surveys, initially at optical wavelengths, and with state-of-the-art information systems for all field objects.

In order to satisfy this requirement, the CDS (Centre de Données astronomiques de Strasbourg) is developing a ‘Deep Sky Mapping Facility’ project, Aladin, which aims to connect the data stored at CDS (astronomical catalogues and Simbad), to pixel data from continuously updated deep optical sky surveys.

Aladin, the Deep Sky interactive Facility, is a new CDS project which provides interactive access to both sky surveys, (starting with optical ones) and also to catalogue data about the studied field objects (Paillou et al. 1993).

The program Pickles was developed as an aid for planning HST observations using the Space Telescope Science Institute's Guide Star Catalogue, which was generated from wide-field Schmidt plates. Pickles reads the catalogue from CD-ROM and then displays a one-degree square field. The HST focal plane apertures can then be displayed singly or in any combination which is at the choice of the observer (Fig. 1). The user can generate an aperture of a different type if need be. The stars can be displayed as open or filled circles with their relative sizes indicating their magnitude. Stars or other objects can be added and saved with the field.

The present status of the work on the creation of a Wide-Field Plate Database is reported. It is planned to collect the available information for about 1.5 million plates from 187 wide-field instruments in 71 institutes/observatories. The source data are from 213 plate catalogues, 65 of them in computer-readable form. The structure and content of the Wide-Field Plate Database, now including 51 observation catalogues with more than 300,000 plates, is presented.

The Harvard College Observatory plate collection is unique in the world in several aspects. First, it is the largest, with a total of approximately half a million plates. Second, because Harvard set up stations very early in the southern hemisphere, the collection covers the entire sky. In fact, the southern hemisphere coverage is slightly better than the northern. Third, the collection is unique in the length of the time interval over which the plates were taken. The first plates were acquired in the northern hemisphere in 1885, and in the southern hemisphere in 1891. There is a substantial gap in the late 1950s and 1960s, but patrol plates were then taken up to 1989. Fourth, the collection contains a very large number of images of a given object. For B = 15 mag or brighter, from several hundred to a thousand or more images can be found; for B = 17.5 mag, one can locate from a few to several hundred images.