A stellar census in globular clusters with MUSE: Multiple populations
  chemistry in NGC 2808
  Galactic globular clusters (GCs) are now known to host multiple populations
displaying particular abundance variations. The different populations within a
GC can be well distinguished following their position in the pseudo two-colors
diagrams, also referred to as "chromosome maps". These maps are constructed
using optical and near-UV photometry available from the Hubble Space Telescope
(HST) UV survey of GCs. However, the chemical tagging of the various
populations in the chromosome maps is hampered by the fact that HST photometry
and elemental abundances are both available only for a limited number of stars.
The spectra collected as part of the MUSE survey of globular clusters provide a
spectroscopic counterpart to the HST photometric catalogs covering the central
regions of GCs. In this paper, we use the MUSE spectra of 1115 red giant branch
(RGB) stars in NGC 2808 to characterize the abundance variations seen in the
multiple populations of this cluster. We use the chromosome map of NGC 2808 to
divide the RGB stars into their respective populations. We then combine the
spectra of all stars belonging to a given population, resulting in one high
signal-to-noise ratio spectrum representative of each population. Variations in
the spectral lines of O, Na, Mg, and Al are clearly detected among four of the
populations. In order to quantify these variations, we measured equivalent
width differences and created synthetic populations spectra that were used to
determine abundance variations with respect to the primordial population of the
cluster. Our results are in good agreement with the values expected from
previous studies based on high-resolution spectroscopy. We do not see any
significant variations in the spectral lines of Ca, K, and Ba. We also do not
detect abundance variations among the stars belonging to the primordial
population of NGC 2808.
