Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey

Abstract

Sky Survey 1 nears completion, preliminary lists are being compiled of some of the many new objects discovered. These lists include more than seventy new planetary nebulae and about a dozen star clusters that are believed to be globular. The Sky Survey covers the entire sky north of-27 degrees declination on both red-and blue-sensitive photographs obtained with the 48-inch Schmidt telescope of the Palomar Observatory. The part of the sky to be surveyed has now been photographed completely, although some fields still must be repeated to obtain plates good enough to meet the high standards set for the survey. The blue exposures are on the Eastman 103a-O emulsion and the red exposures on the Eastman 103a-Ε emulsion in combination with a red Plexiglas filter. The exposure times are chosen to reach the faintest stars which can be recorded by the instrument under average observing conditions. The limiting photographic magnitude of the blue exposures is about 21.1. The computed loss in limiting magnitude due to vignetting in the extreme corners of the 14^ X 14" plates is less than 0.2 magnitude. The image scale is 67.1 seconds of arc per millimeter. Thirteen star clusters have been found on the survey photographs which appear to be globular. They are listed in Table I. Positions of five of these clusters have been published previously ; references are noted in the table. Tabulated for each cluster are its equatorial and galactic coordinates , its apparent diameter on the Schmidt plates, an estimate of the photographic magnitude of its brightest stars, and an estimate of its concentration class.