1 The observational material

The symbiotic star V1329 Cyg had been observed during the years 1979 - 1993 using the 30/150 cm astrograph of the Skalnaté Pleso Observatory. Ninety photographic plates of $9\times12$ cm and $24\times24$ cm formats with emulsions ORWO ZU-2 and ORWO ZU-21 were obtained. The limiting magnitude of the observational material is about 16.5 $m_{\rm pg}$. The resulting magnitude scale is close to the photoelectric B magnitude. The results obtained for this symbiotic star were published by Hric et al. (1993). Because the region thereby investigated is situated only $6\hbox{$^\circ$}$ under the plane of the Milky Way, an idea has originated to make use of the huge amount of the exposed stars on photographic plates for the search of the accessible variable stars with the aim of the determination of their parameters.

Similar research had been underway already in the years 1969 - 1988 at the Asiago Observatory, where 85 photographic plates were obtained using the Schmidt telescope (67/92/215 cm) of the $24\times24$ cm format with the emulsion Kodak 103a-O. The resulting photographic magnitude was close to the photoelectric B magnitude. On the basis of this material, Margoni and Stagni (1984), hereafter MS, and Margoni et al. (1989), hereafter MSMM, found 99 new variable stars in the field under investigation and determined their photographic magnitudes, their light curves (LCs) and, for many of them, also their periods. Thanks to Margoni (1993), who has provided us with his original material in the reduced form, we were able to extend our observational material and almost to double the time interval investigated by us.

During the complex survey of the combined observational material, we have identified and selected 17 variable stars present on almost all the photographic plates and fitting the conditions required for obtaining of photographic magnitudes (the plate's edge, limiting stellar magnitude). We used the findig charts published in MS. Only 3 of those stars were described in the GCVS (Kholopov et al. 1985), further 11 stars were described in The 68th Name-List of Variable Stars (Kholopov et al. 1987). For stars selected that way, we have determined photographic magnitudes through the remeasurement using the iris microphotometer at the Asiago Observatory. Nine stars from the close neighbourhood of V1329 Cygni whose magnitudes were measured by Kohoutek (1969) were used as comparisons, as well as those used as comparisons by MS, 18 objects in total. The list of all comparison stars with B magnitude and source is presented in Table 1. A large number of comparisons should be made to get a better definition of the sensitometric characteristic for each plate as well as to suppress errors of photographic photometry. We used the same finding chart like MS for comparisons and finding chart as well as UBV magnitudes from Grygar et al. (1979) for nine comparisons by Kohoutek (1969). In addition to the stars measured, also the sky level was measured (meaning the combination photographic plate foglevel and the real sky brightness) in the vicinity of each star measured. Almost 3000 measurements (variables, comparisons) were performed.

 

Table 1: The list of comparison stars