Search for a metallicity spread in the multiple population Large
  Magellanic Cloud cluster NGC 1978
  We report on the spread of [Fe/H] values in the massive Large Magellanic
Cloud cluster NGC1978, recently confirmed to harbor multiple populations of
nearly the same age. We used accurate Stromgren photometry of carefully
selected cluster red giant branch stars along with a high-dispersion
spectroscopy-based calibration of the metallicity-sensitive index m1. Once
accounting for the photometry quality, assessed from extensive artificial stars
tests to trace the photometric uncertainties as a function of the position to
the cluster's center as well as the stellar brightness, and those from the
metallicity calibration, we found that NGC1978 exhibits a small metallicity
spread of 0.035 dex (+- 0.019-0.023), depending on whether stars with
individual sigma[Fe/H] < 0.15 dex or those located in the cluster's outer areas
are considered. Such a spread in [Fe/H] is consistent with a cluster formation
model with self-enrichment, if mass loss higher than 90 per cent due to stellar
evolutionary and galactic tidal effects is assumed. Nevertheless, scenarios
where the apparent [Fe/H] variation reflects CN abundance anomalies or less
extreme mass loss models with environmentally-dependent self enrichment should
not be ruled out.
