A large C+N+O abundance spread in giant stars of the globular cluster
  NGC 1851
  Abundances of C, N, and O are determined in four bright red giants that span
the known abundance range for light (Na and Al) and s-process (Zr and La)
elements in the globular cluster NGC 1851. The abundance sum C+N+O exhibits a
range of 0.6 dex, a factor of 4, in contrast to other clusters in which no
significant C+N+O spread is found. Such an abundance range offers support for
the Cassisi et al. (2008) scenario in which the double subgiant branch
populations are coeval but with different mixtures of C+N+O abundances.
Further, the Na, Al, Zr, and La abundances are correlated with C+N+O, and
therefore, NGC 1851 is the first cluster to provide strong support for the
scenario in which AGB stars are responsible for the globular cluster light
element abundance variations.
