1998AJ....116.1736Z

A color-magnitude diagram (CMD) has been constructed for the globular cluster NGC 6139 from V and I photometry. The broad sequences in this CMD are caused by variable interstellar reddening, and a gradient in reddening across the field was measured and removed from the data. From the color and shape of the giant branch, we obtain [Fe/H] = -1.71±0.20 and a mean reddening of E(V-I) = 1.03±0.04 [E(B-V) = 0.76±0.03]. At the blue edge of the instability strip, the mean V magnitude of the horizontal branch is 17.9±0.1. These measurements agree with some but not all previous ones. NGC 6139 has a very blue horizontal branch (HB), (B-R)/(B+V+R) = 0.91±0.06, which appears to be unusually short in color extent compared with other clusters of its high central density and concentration, although additional observations are needed to confirm this. NGC 6139 lies in the inner regions of the Galaxy, but outside the Galactic bulge. Its [Fe/H], HB morphology, and kinematics are typical of other inner halo globular clusters.