Sodium, aluminum, and oxygen abundance variations in giants in the globular cluster M4
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Accurate, quantitative abundances are presented for Fe, Ca, Na, Al, and O in four red giants in the bimodal-CN globular cluster M4. Two of the giants are CN-strong and two are CN-weak: all have very similar magnitudes and colors and, thus, have similar effective temperatures and surface gravities. This analysis utilizes high-resolution, high-SN spectra and up-to-date model atmospheres. For the low-ionization element Na, detailed non-LTE calculations demonstrate that, for lines used in the abundance analysis, departures from LTE are small (≲0.1 dex). As a group, these four M4 giants have homogeneous Fe and Ca abundances, while Na, Al, and O vary: the CN-strong stars have larger Na and Al but smaller O abundances than the CN-weak stars. When compared to field metal-poor stars, the CN-weak stars resemble the field stars, while the CN-strong stars are Na and Al rich.
author list (cited authors)
Drake, J. J., Smith, V. V., & Suntzeff, N. B
complete list of authors
Drake, JJ||Smith, VV||Suntzeff, NB