Observatorio Astronómico de La Plata and Profoeg

Paseo del Bosque, (1900) La Plata, Argentina

1: member of the Carrera del Investigador Científico, Profoeg, CONICET (Argentina)

E-mail: rorellan@fcaglp.fcaglp.unlp.edu.ar

We report the database of 2186 plate archives from the La Plata Observatory: contents, structure and instructions for the user. We hope that this catalogue of plates will be useful for those who are interested in using observations of the Southern Hemisphere.

Keywords: Database - Asteroids - Comets

In the creation of the Working Group (WG) on Wide-field Imaging of the IAU Commission 9, it was unanimously agreed that one of the most important tasks of the new WG would be the creation of a computer-readable form of the plate-catalogue data for all photographic plates existent in observatory archives all over the world (West 1991, 1992; Tsvetkov 1992, 1993, 1994).

The collection of photographic plates at the La Plata Observatory contains a large number of plates taken between 1917 y 1986. All of them have been obtained with the Astrographic Telescope of aperture 343mm and focal length 3.42m.

The data from the direct-photographic observations have been organised as a computer-readable catalogue of plates since 1948. We have available 2031 plates of asteroids and 156 plates of comets, with a field of 2° x 2° on plates of 16cm x 16cm. The coordinate distribution of plates centres by equatorial coordinates largely covers most part of the Southern Hemisphere. The limit of declination is –80°.

The data of our plates have been available in computer-readable form since 1948 to 1986. The plates are stored inside of numbered boxes. The catalogue is written in dBase III plus and contains the following information:

BOX: box number.

DATE: date of exposure beginning of each image.

WB: observation writing book.

PN: plate number in each box.

ASTN: asteroid number.

ANAME: asteroid name.

NAME: comet name.

RAH: hours of right ascension of the plate centre for 1950.0.

RAM: minutes of right ascension of the plate centre for 1950.0.

DG: declination degrees of the plate centre for 1950.0.

DM: minutes of declination of the plate centre for 1950.0.

IN: image number.

ET: exposure time in minutes (asteroids).

ETM: exposure time in minutes (comets).

ETS: exposure time in seconds (comets).

EM: emulsion type.

PQ: plate quality.

A short excerpt from the catalogue is given in Table 1

The data from the observation catalogue have been analysed in order to derive some overall characteristics of the plate archive.

Since 1948, the telescope has been used for direct photography producing 2186 plates.

Figure 1 shows the distribution of plates centres by equatorial coordinates over the sky. We have many plates between right ascension 12hs to 24hs and declination 0° to –60°.

Figure 2 shows the number of plates for each year. The gap between 1964 and 1970 is due to repair operations. The decrease in the number of exposed plates from 1980 is caused by the increasing spurious light due to the fact that the observatory is located inside of the city.

Figure 3 shows the monthly number of plates. The most favourable period for observations was March-September.

Figure 4 shows the plate quality. This information is of major importance for potential users of the archive. The x-axis considers the image quality and plate conditions (VG: very good, G: good, R: regular, B: bad).

Other analysis shows that only the ten percent of all plates have exposure time longer than one hour. The most commonly photographic emulsion type used was 103aO of Kodak.

If a person wishing to use La Plata collection, may be willing to visit La Plata and inspect the corresponding plates by microscope, or coordinate measuring machine.

Questions about the plate collection may be addressed at the La Plata Observatory, e-mail: rorellan@fcaglp.fcaglp.unlp.edu.ar.

It is our purpose to make the plate archive accessible to the whole astronomical community. To this end, in the near future, a network access and digitised plate information are to be implemented.

Acknowledgements The authors wish to thank Dr. Virpi Niemela for her encouragement related to this work. R. P. Di Sisto acknowledges to the Asociación Argentina de Astronomía for a fellowship.

[1] Tsvetkov M.K. 1992, IAU Working Group on Wide-field Imaging Newsleter 2, 51.

[2] Tsvetkov M.K. and Tsvetkova K.P. 1993, IAU Working Group on Wide-field Imaging Newsletter 3, 72.

[3] Tsvetkov M.K., Stavrev K.Y., Tsvetkova K.P., Ivanov P.V. and Iliev M.S. 1994, Proceedings of the IAU Symposium 161: Astronomy from Wide-field Imaging, 359-364.

[4] West R. 1991, The Messenger 65, 45

[5] West R. 1992, IAU Working Group on Wide-field Imaging Newsletter 1, 1.