A. F. Marino, A. P. Milone, C. Sneden, M. Bergemann, R. P. Kraft, G. Wallerstein, S. Cassisi, A. Aparicio, M. Asplund, R. L. Bedin, M. Hilker, K. Lind, Y. Momany, G. Piotto, I. U. Roederer, P. B. Stetson, M. Zoccali
We present an abundance analysis of 101 subgiant branch (SGB) stars in the
globular cluster M22. Using low resolution FLAMES/GIRAFFE spectra we have
determined abundances of the neutron-capture strontium and barium and the light
element carbon. With these data we explore relationships between the observed
SGB photometric split in this cluster and two stellar groups characterized by
different contents of iron, slow neutron-capture process (s-process) elements,
and the alpha element calcium, that we previously discovered in M22’s red-giant
stars. We show that the SGB stars correlate in chemical composition and
color-magnitude diagram position: the stars with higher metallicity and
relative s-process abundances define a fainter SGB, while stars with lower
metallicity and s-process content reside on a relatively brighter SGB. This
result has implications for the relative ages of the two stellar groups of M22.
In particular, it is inconsistent with a large spread in ages of the two SGBs.
By accounting for the chemical content of the two stellar groups, isochrone
fitting of the double SGB suggests that their ages are not different by more
than 300 Myr.
View original:
http://arxiv.org/abs/1202.2825
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