Moscow Astronomical Plate Archives:

Contents, Digitization, Current and Possible Applications

N.N. Samus^1,2, L.A. Sat¹, S.V. Vereshchagin¹, A.V. Zharova²

¹Institute of Astronomy, Russian Academy of Sciences, 48, Pyatnitskaya Str., Moscow 119017, Russia

²Sternberg Astronomical Institute, Moscow University, 13, University Ave., Moscow 119899, Russia

Presented at the international workshop "Virtual Observatories: Plate Content Digitization, Archive Mining and Image Sequence Processing", Sofia, April 2005

Abstract. We describe the astronomical plate archives in Moscow and Zvenigorod and the existing digitization projects. The collection at Sternberg Institute has very valuable parts that can be applied to studies of variable stars and external galaxies and still contain much important information never used yet.

1 Introduction

Regular photographic observations of the sky for variable-star studies were started in Moscow in 1895. Since then, several different telescopes were used to take direct sky plates in and near Moscow, for astrometry and for astrophysics. The Moscow plate archive also contains very important series of direct photographs and objective-prism plates taken at the Sternberg Institute's observatory in Crimea. The direct-plate archive of the Zvenigorod Observatory (Institute of Astronomy of the Russian Academy of Sciences) is less rich but also contains several thousand plates.

2 The Plate Archive of the Sternberg Institute

The contents of the most important Moscow astronomical plate archive, that of the Sternberg Astronomical Institute, was briefly presented in Shugarov et al. [1] in 1999. Since then, the information has been considerably improved. We present its new version in the Table (N is a somewhat rounded number of plates) (In this preprint, the Table was revised compared to the presentation in Sofia and is now still newer compared to [1]). Besides the plate series listed in the Table, the plate archive contains several additional, minor and less important, plate and film series.

THE MOSCOW PLATE COLLECTION (STERNBERG INSTITUTE)

D, cm	F, cm	Field size, deg	mlim	Years	N	Site
10	64	20´28	13 – 14	1895 – 1933	1100	Moscow
16	82	16´22	14	1933 – 1956	2700	Moscow
23	230	6´6		1955 – 1991	10000	Moscow etc.
38	640	1.4´1.4	14	1902 – 1972	6400	Moscow
40	160	10´10	17 – 18	1948 – 1996	22300	Kuchino (near Moscow), Crimea
50	200	3.5´3.5	18 – 19	1958 – 2004	10000	Crimea
50	200	Spectra		1959 – 2004	2300	Crimea
70	1050	0.6´0.6	13 – 18	1961 – 1995	9500	Moscow

All the plates of the Sternberg Institute's collection are kept in sufficiently good conditions, in the vertical position. Some of them (mainly old plates) are in wooden boxes with individual places for each plate, other plates are in card-paper boxes, with soft-paper separators.

The main part of the Sternberg Institute's plate collection, that on variable stars, is kept at Sternberg Institute by a joint team from the department of Galaxy and variable stars of the Sternberg Institute and from the department of unstable stars and stellar spectroscopy of the Institute of Astronomy (Russian Academy of Sciences). The information on these plate series in the Table is quite reliable. Other parts of the collection belong to the Sternberg Institute's department of astrometry and to other teams, we used the information provided by the plate owners. In the description below, we mostly deal with the variable-star plates.

The historically-valuable part of the collection are plates taken with a small equatorial camera with different lenses in 1895--1956. There exist many different plate centers, with overlapping fields and relatively few plates for each of the centers. In the earliest period of the collection, attempts were made to additionally process plates with special chemicals, to ensure better stability of the photographic layer. Currently, we find no difference between the plates thus processed and the rest of the plates: almost no aging problems are detectable among the old Moscow plates.

Obviously, the most scientifically important part of the Sternberg Institute's plate collection are the plates taken with the 40-cm (F=160 cm) astrograph (installed in 1948 in Kuchino near Moscow, moved to Crimea in mid-1950s). This is the astrograph first installed, on the initiative of Prof. C. Hoffmeister, at the Sonneberg Observatory, Germany (where it was called the GA astrograph), in 1938 and taken by the Soviet Union from Germany in 1945 as a part of the war reparations. The telescope's position in Crimea was better than in Sonneberg (to the south in latitude, better weather), and the number of plates taken per year, with a typical exposure time of 45 minutes, approached 900 for the most successful years (see the distribution in Fig.~1). The plates of the astrograph series kept in Moscow are generally of excellent quality and permit detailed studies of many variable stars. The main part of the collection are variable-star fields, from the North Pole to declinations about –30^o, with up to 500 plates per field. For variable stars that can be found in several fields, sometimes we can get as many as 1000 photographic observations. The typical exposure time for the variable-star fields was 45 minutes. The plate limit for such exposures, originally about 17.5–18^m in a system close to B, gradually somewhat deteriorated, mainly because of light pollution problems in Crimea. Besides variable-star fields, a significant part of the series are photographs of galactic globular clusters (with a typical exposure of 30 minutes, or less, down to ~5 minutes in special cases, like studies of bright Cepheids near cluster centers).

Fig. 1. The yearly numbers of plates taken with the Sternberg Institute's 40~cm astrograph.

For decades, the plates from the 40-cm astrograph were extensively used for variable-star research. Nevertheless, the plates still contain a lot of valuable unused scientific information. As an example of scientific treasures waiting to be evaluated for many years, we would like to mention the discovery of the supernova SN 1983ab, visible on 24 plates, by Antipin in 1996 [2, 3].

Also of considerable importance are direct and objective-prism plates taken in the prime focus of the 50-cm Maksutov camera in Crimea. There are also many rich variable-star centers of direct plates in this series, as well as photographs of star clusters and associations. Most direct plates and films from the Maksutov telescope were taken behind filters, in the bands of the UBVR system. The exposure times were from one minute to several hours. An interesting subset of this series are direct plates of the local-group galaxies M 31 (the Andromeda nebula) and M 33 (the Triangulum nebula), taken mainly for discoveries and studies of Novae in these galaxies. This observing project was initiated by Prof. A.S. Sharov before 1970. We have 1853 Maksutov-camera plates of M 31 plus 60 plates of this galaxy taken with the Schmidt telescope at Baldone, Latvia (many more M 31 plates from the Schmidt telescope are kept in the Baldone collection proper) and some 20~plates from other telescopes, including Bulgarian instruments. Our plates of M 31 cover the time interval between 1968 and 2004. These plates of M~31 were used to discover 65 Novae in M 31, to confirm (or not confirm) a number of Novae discovered elsewhere (see, for example, [4]). Currently the project is continued by A. Alksnis (Baldone) and A.~Zharova (Moscow). For M 33, the time interval is 1973–-2004; we have 844 Maksutov plates and 164 plates from the 40-cm astrograph. For the photographs of the galaxies M 31 and M 33, we have the catalog of plates ready in the electronic form.

The quality of the direct plates taken with the Moscow 70-cm Cassegrain reflector (also behind filters, UBVRI) strongly depends on seeing. On poor-seeing nights, individual variable stars were photographed. Excellent-seeing nights were used to study star clusters and variable stars in close double systems, taking advantage of the telescope's large focal length and of the corresponding scale (about 18'' per mm).

3 The Zvenigorod Plate Collection

Besides the Sternberg Institute plate collection, there also exists a plate collection at the Zvenigorod Observatory of the Institute of Astronomy (Russian Academy of Sciences). The plates kept there were taken after 1972 with the Observatory's 40-cm Carl Zeiss astrograph (F=200 cm, field size 8^o×8^o, limiting magnitude down to 18^m on the best plates). The telescope is similar to the GB astrograph of the Sonneberg Observatory. The Zvenigorod plate collection contains about 4500 plates (sky fields of a special-purpose photographic sky survey, asteroids, comets, Pluto, fields of optically identified radio sources). Slightly less than 100 plates from the same telescope, taken for variable-star studies, are contained in the Sternberg Institute's plate collection. There are also some 15000 sky photographs on films in Zvenigorod, taken with a very wide angle (10×150 degrees) satellite-tracking camera.

4 Digitization Projects in Moscow and Zvenigorod

The necessity to digitize our plate collections was correctly understood several years ago. We used the opportunities to learn about the experience gained in the digitizing projects of the Maria Mitchell Observatory (USA), of Italian astronomical institutions, and of the Sonneberg Observatory, made use of digitized plates from foreign observatories in our work (see, for example, [5]).

In December 2004, the Sternberg Institute acquired two CREO Ever Smart Supreme flatbed scanners (Fig. 2) and launched the digitization project. These scanners are very expensive, and their acquisition became possible thanks to special funds provided on the occasion of the 250th anniversary of Moscow University. The scanning area can be as large as 305×432 mm, with the optical resolution up to 5600 dpi. The maximal density is 4.3D. As an operating computer, the scanners require Apple PowerMac G5.

The scanners were installed in an air-conditioned room with stabilized electricity and access to Internet. Currently, we are acquiring equipment for data storage and processing. Extensive experiments have been undertaken in order to select the best scanning mode for our purposes. These experiments are close to their conclusion, and we are planning to start large-scale

scanning in the second half of 2005.

Fig. 2. One of the CREO scanners at the air-conditioned scanner laboratory of the Sternberg Institute.

Earlier in 2004, the Institute of Astronomy purchased two semi-professional Epson Expression 1640~XL scanners. For them, the maximal size of transparent originals is 290×420 mm. The optical resolution is 1600 dpi; in our opinion, such a resolution is insufficient for best-quality direct plates, but it is good enough for many kinds of scanning works in our plate collections. The maximal density is 3.6 D. It is important that the same scanner system is in use in plate collections of several European countries (see contributions in this volume). Such scanners are much cheaper than the CREO scanners, they require Windows PCs, a much more frequently-met computer type at our observatories. Initially, one of the Epson scanners was installed at the Sternberg Institute, but now, with the two CREO scanners working there, both Epson scanners are located at the Zvenigorod Observatory.

The scanning team of the Zvenigorod Observatory maintains a web site (http://skanlab.narod.ru) containing technical information and providing access to low-resolution previews of some scanned plates. So far, the language of this web site is mainly Russian.

The two scanning teams work in a close cooperation. We compare scanning results, jointly discuss scanning modes to be used. It is understood that the most historically and scientifically valuable parts of the Sternberg Institute's plate collection will be scanned with the CREO scanners, at the 2540~dpi resolution, whereas the Zvenigorod plate archive and some less important plates of the Moscow collection will be scanned with the Epson scanners.

Acknowledgments

We are grateful to the organizers for inviting our team to the conference and for possibility of presentation of our projects. Our scanning project is supported, in part, by the Russian Foundation for Basic Research (grants 05-02-16289, 05-02-16688) and by the Program of Support to Leading Scientific Schools of Russia (grant NSh-389-2003-2). Thanks are due to Dr. S. Antipin for his assistance during the preparation of the manuscript.

References

1. S. Shugarov, S. Antipin, N. Samus, and T. Danilkina (1999) Acta Historica Astronomiae 6 81.

2. N. Samus and S.V. Antipin (1996) IAU Circular No. 6439.

3. S.V. Antipin (1996) Comm. 27 and 42 IAU Inform. Bull. Var. Stars No. 4361.

4. A.S. Sharov, A. Alksnis, A.V. Zharova, and Yu.A. Shokin (2000) Astronomy Letters 26 433.

5. P. Kroll, N. Samus, and I. Volkov (2003) Comm. 27 and 42 IAU Inform. Bull. Var. Stars No. 5441.