# On the APOGEE DR14 sodium spread in the Galactic open cluster NGC 188

## TL;DR

This study analyzes the sodium abundance spread in the old open cluster NGC 188 using APOGEE DR14 data, revealing potential multiple populations but highlighting uncertainties and the need for careful spectroscopic analysis.

## Contribution

It provides the first detailed chemical abundance analysis of NGC 188 with a focus on sodium spread and cautions about uncertainties in large spectroscopic surveys.

## Key findings

- Detected a sodium abundance spread of ±0.16 dex among cluster stars.
- Identified a potential anti-correlation between Na and Al/TiII.
- Warned about the impact of measurement uncertainties and analysis pipeline biases.

## Abstract

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.