Chemical and kinematic analysis of CN-strong Metal-poor Field Stars in
  LAMOST DR3
  The large amount of chemical and kinematic information available in large
spectroscopic surveys have inspired the search for chemically peculiar stars in
the field. Though these metal-poor field stars ([Fe/H$]<-1$) are commonly
enriched in nitrogen, their detailed spatial, kinematic, and chemical
distributions suggest that various groups may exist, and thus their origin is
still a mystery. To study these stars statistically, we increase the sample
size by identifying new CN-strong stars with LAMOST DR3 for the first time. We
use CN-CH bands around 4000 \AA~to find CN-strong stars, and further separate
them into CH-normal stars (44) and CH-strong (or CH) stars (35). The chemical
abundances from our data-driven software and APOGEE DR 14 suggest that most
CH-normal stars are N-rich, and it cannot be explained by only internal mixing
process. The kinematics of our CH-normal stars indicate a substantial fraction
of these stars are retrograding, pointing to an extragalactic origin. The
chemistry and kinematics of CH-normal stars imply that they may be GC-dissolved
stars, or accreted halo stars, or both.
