APOGEE-2S Discovery of Light- and Heavy-Element Abundance Correlations
  in the Bulge Globular Cluster NGC 6380
  We derive abundance ratios for nine stars in the relatively high-metallicity
bulge globular cluster NGC 6380. We find a mean cluster metallicity between
[Fe/H]$= -0.80$ and $-0.73$, with no clear evidence for a variation in iron
abundances beyond the observational errors. Stars with strongly enhanced in
[N/Fe] abundance ratios populate the cluster, and are anti-correlated with
[C/Fe], trends that are considered a signal of the multiple-population
phenomenon in this cluster. We detect an apparent intrinsic star-to-star spread
($\gtrsim 0.27$ dex) in the slow neutron-capture process element (s-element) Ce
II. Moreover, the [Ce/Fe] abundance ratio exhibits a likely correlation with
[N/Fe], and a somewhat weaker correlation with [Al/Fe]. If confirmed, NGC 6380
could be the first high-metallicity globular cluster where a N-Ce correlation
is detected. Furthermore, this correlation suggests that Ce may also be an
element involved in the multiple-population phenomenon. Currently, a consensus
interpretation for the origin of the this apparent N-Ce correlation in
high-metallicity clusters is lacking. We tentatively suggest that it could be
reproduced by different channels - low-mass asymptotic giant-branch stars in
the high-metallicity regime or fast-rotating massive stars ("spinstars"), due
to the rotational mixing. It may also be the cumulative effect of several
pollution events including the occurrence of peculiar stars. Our findings
should guide stellar nucleosynthesis models, in order to understand the reasons
for its apparent exclusivity in relatively high-metallicity globular clusters.
