Introduction

The Working Group on Wide-Field Imaging of the IAU Commission 9 "Instruments and Techniques" was established, in July 1991, at 21st IAU General Assembly, in Buenos Aires. It was unanimously agreed that one of the most important tasks of the new WG would be the creation of a computer-readable Data Base, with the existing wide-field  plate archives and all astro-photo plates obtained from the end of last century  until now. In this way, we wish to explain the up-to-date status of the project.

The Wide-field Plate Archives Data Base

The preparation of a list of wide-field plate archives is a necessary step for the creation of the future data base. It is our opinion that the program should be carried out in three stages:

 

1.     Preparation of a list of the wide-field archives -  during 1993;

2.     Computerizing the data base for individual plates in plate archives all over the world - 1993/1996;

3.     Establishing a Data Bank with digitized wide-field plates - after 1996.

 

The first stage was begun with the preparation of the first list of Wide-field Plate Archives. It must, of course, still be done more accurate and complete. We hope to come closer to the goal after sending out this communication, specially prepared for the Latin American Observatories. Once it is reasonably complete and has been thoroughly verified, we believe that it may be reasonable to include this list in the STARCAT and SIMBAD data bases.

 

In parallel to this work, it is reasonable to begin with the next stage - the creation of the data base with the data of the individual plates in the plate archives. We expect to do so on the basis of existing ESO/STECF standard. For this purpose, it is necessary to create first a global catalogue of all known plates. The form of such a catalogue should present the main information, from the separate catalogues of the different observatories, in united computer-readable form. Having in mind the recommendation of B. Hauck (1982) about the information, which ought to be in this catalogue, it would appear that the global catalogue should contain the following information for the general plate parameters:

 

1.     Information about the observatory and the telescope used;

2.     Plate/film designation;

3.     Equatorial coordinates (R.A., D.) of the field center (Equinox);

4.     Size of the plate and angular size;

5.     UT. date or Julian Date and Local Sidereal Time (LST);

6.     Plate type: Direct plate, Multiple exposure, Stellar tracks or Objective Prism (dispersion), Exposure time, Hyper sensitization;

7.     Type of emulsion used and filter;

8.     Comments (Quality, Defects, etc.)

 

It would be advantageous that the organization and the future use of this catalogue would be made according to the conventions adopted for one or more of the existing data bases, e.g. in ESO/STARCAT and Strasbourg. The modification of the used data base management system (DBMS) will play an important role in the efficient progress of the creation of this global catalogue.

 

The main problem, on the way towards the creation of the global catalogue, will be to convert the files of existing plate archives from table-forms to computer-readable forms. Since some wide-field plate archives have, until now, mainly been available in table-form, special attention must be given to this problem. Some observatories have indicated that they have no possibilities, at this moment, to convert their table-form archives into computer-readable ones. However, the Bulgarian Wide-Field Image Group and the Instituto Copérnico's Computer Archives Group have some experience and possibilities in preparing computer catalogues (García et al., 1988 and 1993) and archives. The Bulgarian WFIG has prepared the computer-readable plate archive of the Rozhen Observatory, and could contribute in this direction. The increasing possibilities of the Network communications among the astronomical institutes all over the world, and the increased use of better and better text scanners, for the exchange of information about wide-field astrophotographs, would undoubtedly contribute towards the compilation of a global catalogue for the future data base.

 

The last and most important stage (and certainly the most time- and money-consuming!) of the present project is the creation of the DATA BANK for Wide-field Plate Archives. This part of the project organization can only be started after detailed discussions and the availability of firm financial support. Once realized, it will have brought us all the way through to the practical use and rapid retrieval of information contained within the astronomical WFPA.

 

Only advanced automation and robotization will bring us to the realization of the DATA BANK access which must be accessible to all members of the astronomical community. Storage of the information on optical disks, creation of special software for processing the digitized observational material, transfer of the data after processing to the user are only some basic steps which must be passed on the long way towards the DATA BANK of WFPA. The fast progress in the fields of digitization , the development of ever faster computers and data exchange accessories form the basis of our hope that we are now much closer than we have ever been to this final part of the project.

 

By analyzing the data just compiled today, we can roughly estimate that the total number of all expected wide-field plates is about 2 × 10⁶. If the digitized information, on a medium-size wide-field plate, is 200 MB (megabytes), then, the total information content of these plates will be about 400 TB (terabytes) or no more than 1 PB (10¹⁵ bytes). A very rough - and perhaps optimistic! - estimate of the total time needed for the digitization process of all existing wide-field plates is about 2.5 to 5.0 years of uninterrupted work!

 

To organize, support and access such a large DATA BANK, is a question for the future. In this connection, the archiving experience at STScI-Baltimore and STECF-ESO during creation and data retrieval from Guide Star Catalogue, are good examples from which we can learn how to proceed.

Some comments

At the beginning of the project, last year, the first list of wide field plate archives has now been compiled (Tsvetkov, 1992). 49 observatories and institutes confirm that they possess a total of 174 WFPA related to different instruments. 15 of them are in fully computer readable form and 101 are in the process of preparation - the basis of the future data base.

 

At least 34 observatories /institutes possessing 51 wide-field instruments have not declared their wide-field plate archives. Some of them are from Latin America.

 

From 68 institutes which declared they had possessed photographic plate archives about 5 years ago, 45 are not included in the first list of wide-field plate archives.

 

The future progress of the WFPA work will depend on the speed with which the global catalogue of all wide-field plate archives can be achieved, and later on the means which will be available to produce the DATA BANK with all digitized wide-field plates.

 

Please, collaborate with us sending us, as soon as possible, the following minimum information:

 

1.     Location of Observatory/Institute and a brief description, mainly according to the list of Observatories in the Astronomical Almanac (1992);

2.     East Longitude and Latitude;

3.     Elevation of the Observatory/Institute above sea level;

4.     Telescope parameters: Clear aperture (in meters), diameter of the mirror (if it is the case, in meters), focal length (in meters), scale (in arc seconds), field (in degrees) and type of the telescope (i.e., Schmidt, Astrograph, Reflector; Ritchey-Chrétien);

5.     Year of the beginning of operation or the time of possession of the plate archives;

6.     Information about the type of archive: Plate or Films;

7.     Number of direct and objective prism plates/films;

8.     Information about listings of the archived plates/films: Table-form, computer-readable form or a mix of both.

9.     Name of the astronomer responsible for the plate archive or of the director of the Institute/Observatory.

 

If you can complete the information giving the to-day status of the archiving task, and also if you need some help for to transform table-form to computer-readable form, please include it.

 

References

Garcia, J.R.; Cebral, R.; DiGiorgio, F.; Romano, P.;  Scoccimarro, E.R.; Wahnon, P.; Zimmermann, M.:1988 Bull.Inform.CDS 34, 67.

García, J.R.; Cebral, J.R.;  Scoccimarro, E.R.; Wahnon, P.; Zimmermann, M.; Arena, R.; Bazterra, V.; Pellizza , L.: 1993, Contribuciones del Instituto Copérnico  Vol.2 Nº 2.

Hauck B.: 1982, Automated Data Retrieval in Astronomy, p. 227.

Tsvetkov, M.K.: IAU Commission 9, WGWFI Newsletter No. 2, 51.