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 ∼ 30,000) 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 kinematics 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 (we refer to Milky Way field stars as Milky Way halo field stars unless otherwise specified in this paper) 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 stars with masses around 3–5 M ⊙ .