PALOMAR 10 AND NGC 6749: A STUDY IN CONTRASTS

We present new photometry in V and I for Palomar 10 and NGC 6749, two heavily obscured and sparse globular clusters. The color-magnitude diagram (CMD) of Pal 10 exhibits marked differential reddening with a mean reddening E(B-V) = 1.66 ± 0.1. Its CMD has the purely red horizontal branch characteristic of a high-metallicity cluster; we estimate [Fe/H] ∼ -0.1 on the Zinn-West metallicity scale. NGC 6749 (= Berkeley 42, listed in some other sources as an old open cluster) has a similarly large reddening (E(B-V) = 1.5 ± 0.07) but its CMD is that of a typically metal-poor ([Fe/H] ∼ -1.6) cluster with a purely blue HB. We estimate their distance moduli as (m-M)0 = 13.85 (d = 5.9 kpc) for Pal 10 and (m-M)0 = 14.45 (7.8 kpc) for NGC 6749. King-model fits to their radial distributions yield very low central concentrations for both: c = 0.58 (Pal 10) and c = 0.83 (NGC 6749.