# Chemical and kinematic analysis of CN-strong Metal-poor Field Stars in LAMOST DR3

## TL;DR

This study identifies and analyzes chemically peculiar, metal-poor field stars using LAMOST DR3 data, revealing their potential extragalactic origins and contributions from globular cluster dissolution.

## Contribution

First large-scale identification of CN-strong metal-poor stars in LAMOST DR3, with detailed chemical and kinematic analysis suggesting extragalactic origins.

## Key findings

- Most CH-normal stars are N-rich, not explained by internal mixing.
- A significant fraction of these stars are retrograding, indicating extragalactic origins.
- Chemistry and kinematics suggest they may be GC-dissolved or accreted halo stars.

## Abstract

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.