Exploring the chemical plane of Mg, Mn and Al in the search for extra-galactic stars in the Milky Way

Sammanfattning

In this study, over 2000 Milky Way stars were analyzed in the [Mg/Mn] vs [Al/Fe] chemical plane to identify accreted stars. The Milky Way's faster star formation enriches disk stars with iron-peak elements such as Mn and reduces alpha elements like Mg. Accreted stars, originating from slower star formation rate environments, exhibit lower metallicities, reflected in lower [Al/Fe]. The study evaluates if non local thermodynamic equilibrium (NLTE) modeling, in contrast to local thermodynamic equilibrium (LTE), affects this distinction. Abundances were derived from APOGEE survey data (DR17) for 1944 disk stars and 88 potential accreted stars identified by \cite{Diane}. Spectral synthesis under both LTE and NLTE was performed for 2032 stars, ensuring precise data collection. Diagnostic plots comparing LTE and NLTE abundance determinations revealed discrepancies. While LTE plots showed distinct patterns consistent with theoretical expectations, NLTE plots presented less clear distinctions. NLTE accreted stars exhibited lower [Al/Fe] but not consistently higher [Mg/Mn], indicating NLTE's significant impact on abundance determinations. These findings underscore the importance of NLTE considerations and show that for NLTE calculations, the diagnostic graph is no longer useful.