Constant light element abundances suggest that the extended P1 in NGC
  2808 is not a consequence of CNO-cycle nucleosynthesis
  Recent photometric results have identified a new population among globular
cluster stars. This population, referred to as the ``extended P1'', has been
suggested to be the manifestation of a new abundance pattern where the initial
mass fraction of He changes among cluster stars that share the same CNO values.
The current paradigm for the formation of the multiple stellar populations in
globular clusters assumes that variations in He are the product of chemical
``enrichment'' by the ashes of the CNO-cycle (which changes He and other
elements like C, N and O simultaneously). We obtained MIKE@Magellan spectra of
six giant stars in NGC 2808, a cluster with one of the strongest examples of
the extended P1 population. We provide the first complete characterization of
the light elements abundances for the stars along a significant range of the
extended P1 photometric group. The stars from our sample appear to be
homogeneous in C, N, O, Na, Mg and Al. The lack of a significant change in
these products of the CNO-cycle, suggest that unlike the rest of the
populations identified to date, the photometric changes responsible for the
extended P1 feature are a consequence of an alternative mechanism. Our
measurements, are consistent with the interpretations where the changes of the
He mass fraction among these stars could be consequence of p-p chain
nucleosynthesis (which could increase the He in stars without affecting heavier
elements). Having said that, direct measurements of He are necessary to
conclude if variations of this element are present among extended P1 stars.
