Chemical analysis of Asymptotic Giant Branch stars in M62
  We have collected UVES-FLAMES high-resolution spectra for a sample of 6
asymptotic giant branch (AGB) and 13 red giant branch (RGB) stars in the
Galactic globular cluster M62 (NGC6266). Here we present the detailed abundance
analysis of iron, titanium, and light-elements (O, Na, Al and Mg). For the
majority (5 out 6) of the AGB targets we find that the abundances, of both iron
and titanium, determined from neutral lines are significantly underestimated
with respect to those obtained from ionized features, the latter being,
instead, in agreement with those measured for the RGB targets. This is similar
to recent findings in other clusters and may suggest the presence of Non-Local
Thermodynamical Equilibrium (NLTE) effects. In the O-Na, Al-Mg and Na-Al
planes, the RGB stars show the typical correlations observed for globular
cluster stars. Instead, all the AGB targets are clumped in the regions where
first generation stars are expected to lie, similarly to what recently found
for the AGB population of NGC6752. While the sodium and aluminum abundance
could be underestimated as a consequence of the NLTE bias affecting iron and
titanium, the used oxygen line does not suffer from the same effects and the
lack of O-poor AGB stars therefore is solid. We can thus conclude that none of
the investigated AGB stars belong to the second stellar generation of M62. We
also find a RGB star with extremely high sodium abundance ([Na/Fe] = +1.08
dex).
