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Session 82 - Globular Clusters.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
We have observed two red giants in each of the young globular clusters Ruprecht 106 and Pal 12 with the CTIO 4m echelle and analyzed the spectra for chemical composition. We find for Rup 106 [Fe/H] \simeq -1.5, [O/Fe] \simeq 0.0, and [\alpha/Fe] \simeq -0.2. For Pal 12 we find [Fe/H] \simeq -1.0 and [\alpha/Fe] \simeq -0.05; we have no information on oxygen in Pal 12. The light odd-Z metals Na and Al are both overdeficient in both clusters' stars. The stars are all CN-weak compared to similar giants in nearby globulars of comparable [Fe/H]. The abundance results for Rup 106 rule out the possibility that the apparent youth of the cluster as derived from its color-magnitude diagram is caused by an anomalous composition; the lack of results for oxygen prevent us from making a similar statement for Pal 12. These abundances imply a very different star formation history for the material from which these clusters formed, compared to the well-studied old nearby globulars, and are consistent with the suggestion that these clusters are accreted objects, and were not formed in the same environment as the old clusters.
Program listing for Wednesday