NGC 6144 BVI photometry

This cluster is located in the direction of the {rho} Ophiuchi dust cloud, approximately 30 northwest of the bright star {alpha} Scorpii (Antares). Our color-magnitude diagrams (CMDs) of NGC 6144 extend from above the tip of the first-ascent red giant branch (RGB) to ~3mag below the horizontal branch (HB).

The morphology of the HB is predominantly blueward of the RR Lyrae instability strip, while the RGB is relatively steep, signifying a low-to-intermediate metal abundance. Our CMD also reveals the presence of three candidate post-asymptotic giant branch stars. We find VHB=16.30+/-0.07; coupling the measured RGB color at the level of the HB with a polynomial describing the shape of the RGB, we have utilized the simultaneous reddening and metallicity method of Sarajedini to estimate a metallicity of [Fe/H]=-1.81+/-0.12 (on the Zinn & West, 1984ApJS...55...45Z, scale) and a mean reddening of E(B-V)=0.41+/-0.02.