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Description
We present broadband B,V photometry for 1154 stars in the field of the Galactic globular cluster Palomar 12, based upon direct CCD images obtained with the Canada-France-Hawaii 3.6m and Cerro Tololo 4m telescopes. The overall zero points of our V magnitudes and B-V colors appear to be known to about +/-0.02mag and +/-0.01mag, and our magnitude- and color-scale errors are probably controlled to <0.01mag. Pal 12's main sequence shows an excess fringe of stars along its red edge which are probably binaries; the CM diagram also contains a small number of probable blue stragglers. The principal result of this paper is that the color-magnitude diagram of Pal 12 is anomalous, in the sense that we cannot fake all of its principal sequences lie near or between those of the well studied and presumably typical Galactic globular clusters 47 Tucanae and M5, even though it lies near or between them in overall heavy-element abundance. The simplest explanation is that Pal 12 is younger than the other two clusters by some 25-30%. Other explanations are also possible, although perhaps somewhat harder to believe. This result greatly strengthens the possibility that age differences are responsible, at least in part, for the anomalous properties of some of the outer-halo globular clusters. Spectroscopic indications are that Pal 12's chemical abundances should also strongly resemble those of the two Galactic globular clusters NGC 288 and NGC 362, which have also been claimed to show age differences in comparison with M5. However, attempts to derive ages for these clusters relative to M5 and Pal 12 are inconclusive, possibly due to some inconsistencies within the available data.
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