On the APOGEE DR14 sodium spread in the Galactic open cluster NGC 188
  Since several years ago, the search for multiple populations (MPs) in
Galactic open clusters (OCs) has become a field of increasing interest,
particularly to the light of the general knowledge that MPs are observed in
relatively massive clusters (>= 5 10^4 Mo). I report here measurements of
stellar parameters and abundances of 17 different chemical species, including
light and iron-peak elements of the old open cluster NGC188, from the APOGEE
DR14 database. I selected 15 bonafide cluster red giants that reveal an spread
in [Na/Fe] of +-0.16 dex, caused by two different groups of measurements whose
mean [Na/Fe] values differ by ~ 0.30 dex. A hint for a subtle anti-correlation
with Al and TiII, which also show relative large [X/Fe] dispersions, is also
seen in the data. However, [Na/Fe] abundances have been found to be typically
affected by uncertainties of 0.16 dex. Furthermore, I directly compared the
available spectra for stars with similar atmospheric parameters and it would
seem that they look similar. Therefore, I warn users of large spectroscopic
surveys to be extra careful when finding peculiar abundance results. Analysis
pipelines that run in an unsupervised fashion may produce bad results which may
not be noticed before publication.
