On the discovery of K-enhanced and possibly Mg-depleted stars throughout
  the Milky Way
  Stars with unusual elemental abundances offer clues about rare astrophysical
events or nucleosynthetic pathways. Stars with significantly depleted magnesium
and enhanced potassium ([Mg/Fe] < -0.5; [K/Fe] > 1) have to date only been
found in the massive globular cluster NGC 2419 and, to a lesser extent, NGC
2808. The origin of this abundance signature remains unknown, as does the
reason for its apparent exclusivity to these two globular clusters. Here we
present 112 field stars, identified from 454,180 LAMOST giants, that show
significantly enhanced [K/Fe] and possibly depleted [Mg/Fe] abundance ratios.
Our sample spans a wide range of metallicities (-1.5 < [Fe/H] < 0.3), yet none
show abundance ratios of [K/Fe] or [Mg/Fe] that are as extreme as those
observed in NGC 2419. If confirmed, the identified sample of stars represents
evidence that the nucleosynthetic process producing the anomalous abundances
ratios of [K/Fe] and [Mg/Fe] probably occurs at a wide range of metallicities.
This would suggest that pollution scenarios that are limited to early epochs
(such as Population III supernovae) are an unlikely explanation, although they
cannot be ruled out entirely. This sample is expected to help guide modelling
attempts to explain the origin of the Mg-K abundance signature.
