Refinement of the FOCAT Catalog in the Declination Zone from -10 To -18 Degrees

In 1978 the Pulkovo Observatory initiated southern sky observations (in the declination range from -8 to -20 deg) at the Zelenchuk station of the Engelhardt Astronomical Observatory with the aim of producing a catalog of positions of stars down to 10th or 11th magnitude, to be used in further refinement of the existing FOCAT catalog. Observations were performed using the Zeiss astrograph with a four-fold overlap pattern. Observations of the zone under study were made using 300 x 300 mm plates covering a 4 x 4 deg field on the sky. The mean epoch of observations is 1979. The average star density within the sky zone studied is about one star per square degree. The method of astrometric reduction that we have used involves the determination of the coordinates of the optical center and the tangent points of the plates, and the coefficients of radial cubic distortion in both coordinates. The corresponding reduction formulas include 10 to 12 constants. We used the spherical coordinates from the PPM catalog to calculate the standard coordinates by successive approximations. (Abstract only). (Author)