SCHMIDT PLATE SURVEY IN THE GALACTIC-CENTER DIRECTION .1. INVESTIGATION OF OPEN CLUSTERS IN THE SAGITTARIUS-CARINA SPIRAL ARM

A study of four open clusters on Tautenburg Schmidt plates in the dire ction to the Galactic Centre (l = 17.0 degrees, b = +0.8 degrees) is p resented. In a field of 8.95 square degrees proper motions and B, V ma gnitudes were determined for about 36 500 stars up to the limiting mag nitudes B = 17(m)9, V = 16(m)8. For stars brighter than B = 16(m) an a ccuracy of about 3 mas/year has been estimated for proper motions. The rms errors of stellar magnitudes and (B - V) colours is about 0.1 mag . There are two open clusters already known in this sky area: Trumpler 32 (C 1814-133) and NGC 6611 (C 1816-138). By the inspection of the p lates two additional anonymous clusters were identified near the doubl e star ADS 11285 or ED -14 degrees 5014 (C 1819-146) and near the star BD -14 degrees 5016 (C 1820-146). The cluster membership determinatio n was carried out using information on spatial and proper motion distr ibutions of stars in the field. The colour-magnitude diagrams up to th e limiting stellar magnitude were constructed. For each cluster inters tellar extinction Av, diameters of the core and corona, ages and spati al velocity components (V, W) relative to the LSR in the Y,Z-galactic directions were derived. The distances to the clusters were obtained t o 1720 pc, 2260 pc, 2130 pc and 2130 pc for Trumpler 32, NGC 6611, C 1 819-146 and C 1820-146, respectively All clusters are situated in the Sagittarius-Carina spiral arm. Their spatial location confirms the ass umption that galactic spiral arms are close to logarithmic spirals wit h a characteristic angle of about 20 degrees.