NGC6218 :: new paper
|Johnson, Christian I.; Pilachowski, Catherine A.|
A Moderate Sample Size, Multielement Analysis of the Globular Cluster M12 (NGC 6218)
We present chemical abundances of several proton-capture, α-, Fe-peak, and neutron-capture elements and radial velocities for 21 red giant branch (RGB) and asymptotic giant branch members of the Galactic globular cluster M12. Abundances are based on equivalent width measurements and synthetic spectral analyses of moderate-resolution spectra (R~15,000) obtained with the 3.5 m WIYN telescope and Hydra multifiber spectrograph. The stars observed range from the RGB tip (M0v=-2.47) down to about 0.50 mag above the level of the horizontal branch (M0v=+0.11). Our spectroscopic analysis suggests that M12 is a moderately metal-poor cluster with [Fe/H]=-1.54 (σ=0.09). While the Na abundances exhibit a range of 0.90 dex, Mg and Al abundances are enhanced by 0.37 and 0.54 dex and are nearly constant at all RGB luminosities, in contrast to the blue horizontal-branch cluster M13. The α- and Fe-peak elements indicate that M12 has undergone a similar chemical enrichment history to that of globular clusters and field stars of comparable metallicity, with <[α/Fe]〉=+0.33 (σ=0.11). M12 also appears to be slightly r-process-rich, with <[Eu/Ba,La]〉=+0.22 (σ=0.18).
The Astronomical Journal, Volume 132, Issue 6, pp. 2346-2359