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Unveiling Palomar 2: The Most Obscure Globular Cluster in the Outer Halo

W. E. Harris·P. R. Durrell·G. R. Petitpas·T. M. Webb·S. C. Woodworth
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Abstract

We present the first color-magnitude study for Palomar 2, a distant and heavily obscured globular cluster near the Galactic anticenter. Our (V,V-I) color-magnitude diagram (CMD), obtained with the UH8K camera at the CFHT, reaches V(lim) = 24 and clearly shows the principal sequences of the cluster, though with substantial overall foreground absorption and differential reddening. The CMD morphology shows a well populated red horizontal branch with a sparser extension to the blue, similar to clusters such as NGC 1261, 1851, or 6229 with metallicities near [Fe/H] = -1.3$. From an average of several indicators, we estimate the foreground reddening at E(B-V) = 1.24 +- 0.07 and obtain a true distance modulus (m-M)_0 = 17.1 +- 0.3$, placing it about 34 kpc from the Galactic center. We use starcounts of the bright stars to measure the core radius, half-mass radius, and central concentration of the cluster. Its integrated luminosity is M_V = -7.9, making it clearly brighter and more massive than most other clusters in the outer halo.

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W. E. Harris, P. R. Durrell, G. R. Petitpas, T. M. Webb, S. C. Woodworth. 1997-07-03. Unveiling Palomar 2: The Most Obscure Globular Cluster in the Outer Halo. https://doi.org/10.1086/118534

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