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B. Chaboyer, M.S. Lewis, W.M. Liu, N.E.Q. Paust (Dartmouth College)
We present new photometry for the Galactic thick disk globular cluster Palomar 11 extending well past the main sequence turn-off in the V and I bands. This photometry shows noticeable, but depleted red giant and subgiant branches. The difference in magnitude between the red horizontal branch (red clump) and the subgiant branch is used to determine that Palomar 11 has an age of 10.4±0.5 Gyr. The red clump is used to derive a distance d\odot=14.3±0.4 kpc, and a cluster reddening of E(V-I)=0.40±0.03. The colour magnitude diagram of Palomar 11 is virtually identically to the thick disk globular cluster NGC 5927, implying that these two clusters have a similar age and metallicity. Palomar 11 has a slightly bluer red giant branch than 47 Tuc, implying that Palomar 11 is 0.15 dex more metal-rich, or 1 Gyr older than 47 Tuc. Ca II triplet observations (Rutledge et al.\ 1997, PASP, 109, 907) favour the hypothesis that Palomar 11 is the same age as 47 Tuc, but slightly more metal-rich.
Research supported in part by a NSF CAREER grant 0094231 to BC. BC is a Cottrell Scholar of the Research Corporation.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.