The close relationship between the nature of the Triangulum-Andromeda ( TriAnd ) overdensity and the Galactic disk has become increasingly evident in recent years .
However , the chemical pattern of this overdensity ( R _ { GC } = 20 - 30 kpc ) is unique and differs from what we know of the local disk .
In this study , we analyze the chemical abundances of five \alpha elements ( Mg , O , Si , Ca , and Ti ) in a sample of stars belonging to the TriAnd overdensity , including stars with [ Fe/H ] < - 1.2 , to investigate the evolution of the \alpha elements with metallicity .
High-resolution spectra from Gemini North with GRACES were analyzed .
Overall , the TriAnd population presents an \alpha -element pattern that differs from that of the local disk ; the TriAnd stars fall in between the local disk and the dwarf galaxies in the [ X/Fe ] vs. [ Fe/H ] plane .
The high [ Mg/Fe ] ratios obtained for the lower metallicity TriAnd stars may indicate a roughly parallel sequence to the Milky Way local disk at lower values of [ Fe/H ] , revealing a ’ knee ’ shifted towards lower metallicities for the TriAnd population .
Similar behavior is also exhibited in the [ Ca/Fe ] and [ Si/Fe ] ratios .
However , for O and Ti the behavior of the [ X/Fe ] ratios shows a slight decay with decreasing metallicity .
Our results reinforce the TriAnd overdensity as a unique stellar population of the Milky Way , with an abundance pattern that is different from all stellar populations studied to date .
The complete understanding of the complex TriAnd population will require high-resolution spectroscopic observations of a larger sample of TriAnd stars .