UBV photometry of the open clusters NGC 6604 and NGC 6704

Abstract

The open clusters NGC 6604 and NGC 6704 have been studied with UBV photoelectric and photographic photometry, resulting in improved distance and color-magnitude diagrams. NGC 6604 is a very young (~4x 10 [supercript 6] yr) cluster with 30 probable members. The color-magnitude diagram shows a bright, well-defined main sequence; the central star of the cluster, HD 167971, is an O8f supergiant which appears to be slightly evolved. The fainter stars with (B-V)[subscript 0][greater than or equal to] 0.0 appear to lie above the zero-age main sequence and may be pre-main-sequence objects still in the process of gravitational contraction. This result must be confirmed because of the uncertainty in the photometric calibration near V=16 mag. NGC 6704 is a moderately young (~2x10[superscript 7] yr) cluster with 17 probable members observed, including the eclipsing binary FN Sct. The color-magnitude diagram shows a fairly well-defined main sequence, but no giant members are observed.