Palomar 12 as a Part of the Sagittarius Stream: The Evidence from Abundance Ratios

We present a detailed abundance analysis for 21 elements based on high-dispersion, high spectral resolution Keck spectra for four members of the outer halo ``young'' Galactic globular cluster Palomar 12. All four stars show identical abundance distributions with no credible indication of any star-to-star scatter. However, the abundance ratios of the Pal 12 stars are very peculiar. There is no detected enhancement of the α-elements the mean of [Si/Fe], [Ca/Fe], and [Ti/Fe] is -0.07+/-0.05 dex, O/Fe is also solar, while Na is very deficient. The distribution among the heavy elements shows anomalies as well. These are inconsistent with those of almost all Galactic globular clusters or of field stars in the Galaxy. The peculiarities shown by the Pal 12 stars are, however, in good general agreement with the trends established by Smecker-Hane & McWilliam and by Bonifacio et al. for stars in the Sagittarius dwarf spheroidal (dSph) galaxy evaluated at the [Fe/H] of Pal 12. This reinforces earlier suggestions that Pal 12 originally was a cluster in the Sgr dSph galaxy that during the process of accretion of this galaxy by our own was tidally stripped from the Sgr galaxy to become part of the extended Sgr stream.

Based in part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.