UBVRI and Hα Photometry of the Young Open Cluster NGC 6530

Abstract

New UBVRI and Hα photometry has been obtained for the young open cluster NGC 6530 located 10' east of the Lagoon Nebula (M8). We found 37 pre-main-sequence (PMS) stars with Hα emission and nine PMS candidates using the R-Hα color, a measure of Hα emission. From this new photometry we derived the cluster parameters (V₀-M_V=11.25+/-0.1 mag and <E(B-V)>=0.35 mag), typical age (1.5 Myr), and an age spread of about 5 Myr. We confirmed the presence of a small amount of differential reddening across the cluster. We also verified the abnormal reddening law for the cluster, especially for a heavily embedded O7 V star, Herschel 36. Comparisons were made for several PMS evolution models with regard to the resulting age distribution and the initial mass function.