Abstract
In Martell & Grebel (2010) we reported the discovery in the Sloan Digital Sky Survey-II/SEGUE spectroscopic database of a small subset of halo red giants, 2.5%, with CN and CH band strengths indicative of globular-cluster-like carbon and nitrogen abundances. Because the formation of stars with unusual light-element abundances is thought to be restricted to high-density environments like globular clusters, this result has strong implications for both cluster formation processes and the assembly history of the Galactic halo. Here we discuss two efforts to expand upon that work.
Highlights
Globular clusters in the Milky Way all contain clear light-element abundance variations (e.g., [2,3,4,5])
In [1] we reported the discovery in the Sloan Digital Sky Survey-II/SEGUE spectroscopic database of a small subset of halo red giants, 2.5%, with CN and CH band strengths indicative of globularcluster-like carbon and nitrogen abundances
Because the formation of stars with unusual light-element abundances is thought to be restricted to high-density environments like globular clusters, this result has strong implications for both cluster formation processes and the assembly history of the Galactic halo
Summary
Globular clusters in the Milky Way all contain clear light-element abundance variations (e.g., [2,3,4,5]). The typical pattern is C-N, O-Na and Mg-Al anticorrelations, with roughly half of the stars having scaled-Solar abundances and half showing a range of depletions in C, O and Mg and enhancements in N, Na and Al. The typical pattern is C-N, O-Na and Mg-Al anticorrelations, with roughly half of the stars having scaled-Solar abundances and half showing a range of depletions in C, O and Mg and enhancements in N, Na and Al This pattern is presently interpreted as a sign that stars in globular clusters are formed in two closely spaced generations. Light-element abundance variations are found in all Galactic globular clusters, they have not been found in open clusters (e.g., [9,10,11]), lending weight to the idea that the high density of early globular clusters permitted a partial self-enrichment, and indicating that unusual light-element abundances can be used to identify stars that originally formed within globular clusters, even after those clusters have been disrupted through tidal interactions with the Galaxy or evaporated through internal two-body interactions
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