A QUANTITATIVE ANALYSIS OF DISTANT OPEN CLUSTERS

The oldest open star clusters are important for tracing the history of the Galactic disk, but many of the more distant clusters are heavily reddened and projected against the rich stellar background of the Galaxy. We have undertaken an investigation of several distant clusters (Berkeley 19, Berkeley 44, King 25, NGC 6802, NGC 6827, Berkeley 52, Berkeley 56, NGC 7142, NGC 7245, and King 9) to develop procedures for separating probable cluster members from the background field. We next created a simple quantitative approach for finding approximate cluster distances, reddenings, and ages. We first conclude that with the possible exception of King 25 they are probably all physical clusters. We also find that for these distant clusters our typical errors are about +/- 0.07 in E(B - V), +/- 0.15 in log(age), and +/- 0.25 in (m - M)(circle dot). The clusters range in age from 470 Myr to 7 Gyr and range from 7.1 to 16.4 kpc from the Galactic center.