Baltic Astronomy, vol. Ί, 653-668, 1998. BALDONE SCHMIDT TELESCOPE PLATE ARCHIVE AND CATALOGUE A. Alksnis, A. Balklavs, I. Eglitis and 0. Paupers Institute of Astronomy, University of Latvia, Raina bulv. 19, Riga LV-1586, Latvia Received November 20, 1998. Abstract. The article presents information on the archive and catalogue of the astrophotos taken with the Schmidt telescope of the Institute of Astronomy of the University of Latvia (until July 1, 1997 - Radioastrophysical Observatory of the Latvian Academy of Sciences) in the period 1967-1998. The archive and catalogue contain more than 22 000 direct and 2300 spectral photos of various sky regions. Information on the types of photo materials and color filters used as well as on most frequently photographed sky fields or objects is given. The catalogue is available in a computer readable form at the Institute of Astronomy of the University of Latvia and at the Astrophysical Observatory in Baldone (Riekstukalns, Baldone, LV-2125, Latvia), e-mail: [email protected]. Key words: catalogs: plate archive - telescopes: Baldone Schmidt - methods: observational 1. INTRODUCTION One of the main tasks of astronomers is to obtain observational data on various objects of the Universe and preserve these data for their use in future. Initially the observational data in the direct or treated form were kept in paper records, later on as printed catalogs stored in libraries. For more than 100 years astronomers have gath- ered and stored in plate archives the information directly recorded on photographic emulsion layer of glass or film plates. 654 A. Alksnis, Α. Balklavs, I. Eglitis, O. Paupers Table 1. The largest Schmidt telescopes. Observatory The entrance Acting since Country aperture year (cm) Palomar 122 1947 U.S.A. Bloemfontein 81 1950 South Africa Hamburg - Calar Alto 80 1955 Germany Tautenburg 134 1960 Germany Byurakan 100 1961 Armenia Kvistaberg 100 1964 Sweden Baldone 80 1967 Latvia La Silla 100 1969 ESO, Chile Siding Spring 124 1973 Australia Kiso 105 1974 Japan Merida 100 1976 Venezuela Calern 90 1976 France For more than 30 years such an astronomical plate archive (or glass library) of photographic negatives, obtained with the Baldone Schmidt telescope is being collected at the Astrophysical Observa- tory of the Institute of Astronomy, University of Latvia (until July 1, 1997 - Radioastrophysical Observatory of the Latvian Academy of Sciences). The Baldone Schmidt telescope (80/120/240 cm) was put into operation in December 1966 on the Riekstukalns hill (Λ = +24° 24.0', b = 56° 47', altitude h = 75 m) near Baldone town. The telescope still resides among the 12 largest wide field Schmidt tele- scopes in the world (Table 1). The first astronomical photos were obtained in January 1967 (Alksnis 1976). They cover a field of 4° 46' in diameter, the size of photoplates is 24 χ 24 cm. The optical characteristics of the telescope are described by Paupers (1971) and Alksnis (1973b). The scientific interests of the Latvian astronomers in the field of stellar astronomy from the very beginning were directed mainly to carbon stars (see, for example, Alksne L· Ikaunieks 1981, Alksne, Alksnis & Dzërvïtis 1991 and references therein, and several review papers: Balklavs 1971, 1976, 1986, 1987). Therefore, the major- ity of plates, both direct and spectral, obtained with the Baldone Schmidt telescope plate archive 655 Schmidt telescope, cover the zone along the galactic equator, where the galactic carbon stars are concentrated (Figs. 1 and 2). According to the data of the IAU Commission 9 Working Group on Wide Field Imaging (now the Working Group on Sky Surveys) in the wide-field plate archives of the observatories all over the world in 1994 there were more than 1.7 million wide-field plates of which more than 380 000 have been obtained with Schmidt telescopes including more than 20 000 - with the Baldone Schmidt telescope (Tsvetkov et al. 1995). In the last 20 years the digitalization of astronomical informa- tion is progressing. At present the observational data and treated results are obtained in a computer readable form mainly online and stored in data bases. Nevertheless, the value of astronomical plate archives does not decrease: they contain information in the optical range of the former changes of cosmic objects, investigations of which have become especially important at present, when astronomers are gaining information in the whole range of electromagnetic spectrum from gamma to radio waves. 2. PLATE ARCHIVE Each plate of the Baldone Schmidt telescope has been taken in order to study a definite cosmic object or group of objects, therefore only for these objects either brightness or coordinates on the plates have been measured. Usually about 95% to 99% of the information recorded on the emulsion layer of plate remain unused. However, in future this information might be very important for other investiga- tions. Therefore, these plates have to be stored at least until they will be scanned and transformed to a computer readable form. Unfortunately the Baldone Observatory has no special deposi- tory for the plate archive. The glass and film plates are stored ver- tically in the rooms of the Schmidt telescope dome, where they are less subjected to rapid temperature variations. The plates are placed in the original ORWO 24 x 24 cm size plate packing boxes, arranged on shelves in the chronological sequence. A small percentage of the archive plates are in use by people of various astronomical research institutions, mainly by those, who participated in the photographing process. Photos of the Baldone Schmidt telescope archive have been ob- tained mainly on the ORWO (East Germany) astronomical plates 656 A. Alksnis, Α. Balklavs, I. Eghtis, O. Paupers Fig. 1. All-sky distribution of the 22 000 direct exposures, made with the Baldone Schmidt telescope, plotted in equatorial coordinates in equal-area projection. 12 — 90c Fig. 2. All-sky distribution of the 2300 spectral exposures (as in Fig. 1). Schmidt telescope plate archive 657 1400 1200 1000 800 600 400 200 0 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 Fig. 3. Distribution by time (years) of the number of photos (the lighter shaded columns) and of the sum of duration (in hours) of exposures (the darker shaded columns) obtained with the Baldone Schmidt telescope in the period 1967-1998. (Astro Platten ZU1, ZU2, ZU21, ZP1, ZP3) of the 24 x 24 cm size and on the film plates (different versions of A500, A600, A700) of the Photographic Research Institute in Kazan (Russia), but a small quantity - on the Eastman Kodak plates (mainly IN). Since 1995, the plates NT-1AS (Mikhailov & Sheglov 1994), made in Pereyaslavl- Zalessky (Russia) and hypersensitized in hydrogen, have been used. For stellar photometry, the plates and light filters have been used to accomplish the passbands of standard photometric systems: the U, Β, V passbands, the Becker R passband and the Krön I passband (Alksnis 1973a, Alksnis, Alksne L· Daube 1973, Duncans 1979). In Table 2 the numbers η of direct photos taken with the most frequently used emulsion type and filter combinations are listed. The information on different types of photo emulsions used in astronomy is gathered in the recent book by Dokuchaeva (1995). Spectral plates have been obtained using 2° and 4° objective prisms of the 80 cm diameter, which provide the reciprocal dispersion of 1130 Â/mm, resp. 600 Â/ mm at the hydrogen H7 line (Alksne et al. 1989). Various combinations of filters and emulsion types have been used taking into consideration the necessary wavelength range. 658 A. Alksnis, Α. Balklavs, I. Eghtis, O. Paupers Table 2. Combinations of the photo emulsions and filters most frequently used for the direct plates. Emulsion Filter η Emulsion Filter η - U ZU21 — 262 ZU21 UG1 337 ZU1 - 119 ZU2 UG1 229 ZP3 - 21 ZU21 UFS3 87 A500N - 20 ZU1 UG1 62 Β V ZU21 GG13 2703 A600N ZhS17 2101 ZU2 GG13 1691 A600 ZhS17 1799 NT-1AS GG13 207 A600U ZhS17 380 A500N GG13 204 A600RP ZhS17 219 R I ZP1 RG1 7014 IN KS19 848 ZP1 KS13 1577 IN RG1+BG3 441 ZP3 RG1 739 1840 RG1 26 A700N KS13 240 IVN KS19 10 For the search of carbon stars, the orthochromatic Kazan A600 astro films and the Kodak IN infrared plates were mostly used (Table 3). In total more than 160 various combinations of filters and photo emulsions for direct photos and more than 110 combinations for spec- tral photos were used. Many of the sky regions have been photographed tens and some of them even hundreds of times, in order to investigate variability of stars. Most frequently photographed objects or regions are listed in Table 4 (for direct plates) and Table 5 (for spectral plates) with the total number of plates η of the object obtained in 1967-1998. Fig. 3 shows the distribution of the number of the Baldone Schmidt telescope photos by time in years (lighter shaded columns) and of the corresponding sum (hours) of exposure duration (darker shaded columns). During the first five years of the telescope Schmidt telescope plate archive 659 Table 3. Combinations of photo emulsions and filters mostly used for the spectral photos. Emulsion Filter η Emulsion Filter η Blue spectrum Yellow spectrum A600 GG13 98 A600 - 403 ZU2 - 68 A600N GG5 167 ZU21 - 33 A600N - 139 A600N GG13 31 A600 GG5 120 Red spectrum Infrared spectrum 103aF - 123 IN RG1 158 103aF RG1 45 IVN - 43 A700F - 41 IN - 37 A700N — 37 1840 — 32 operation (1967-1971) the number of photos obtained annually grad- ually reached a level of 800. From 1975 to 1988 it was still higher and varied about the average value of 1100. Continuous and fast decline is seen after 1988.