Chemical Tagging N-rich Field Stars with High-resolution Spectroscopy

Abstract

We measure chemical abundances for over 20 elements of 15 N-rich field stars with high resolution (R ∼ 30000) optical spectra. We find that Na, Mg, Al, Si, and Ca abundances of our N-rich field stars are mostly consistent with those of stars from globular clusters (GCs). Seven stars are estimated to have [Al/Fe] > 0.5, which is not found in most GC "first generation" stars. On the other hand, α element abundances (especially Ti) could show distinguishable differences between in situ stars and accreted stars. We discover that one interesting star, with consistently low [Mg/Fe], [Si/Fe], [Ca/Fe], [Ti/Fe], [Sc/Fe], [V/Fe], and [Co/Fe], show similar kinematic and [Ba/Eu] as other stars from the dissolved dwarf galaxy "Gaia-Sausage-Enceladus". The α-element abundances and the iron-peak element abundances of the N-rich field stars with metallicities −1.25 ≤ [Fe/H] ≤ −0.95 show consistent values with Milky Way field stars a) rather than stars from dwarf galaxies, indicating that they were formed in situ. In addition, the neutron capture elements of N-rich field stars show that most of them could be enriched by asymptotic giant branch (AGB) stars with masses around 3 − 5 M .