The SDSS-IV Apache Point Observatory Galactic Evolution Experiment ( APOGEE ) survey provides precise chemical abundances of 18 chemical elements for \sim 176,000 red giant stars distributed over much of the Milky Way Galaxy ( MW ) , and includes observations of the core of the Sagittarius dwarf spheroidal galaxy ( Sgr ) .
The APOGEE chemical abundance patterns of Sgr have revealed that it is chemically distinct from the MW in most chemical elements .
We employ a k -means clustering algorithm to 6-dimensional chemical space defined by [ ( C+N ) /Fe ] , [ O/Fe ] , [ Mg/Fe ] , [ Al/Fe ] , [ Mn/Fe ] , and [ Ni/Fe ] to identify 62 MW stars in the APOGEE sample that have Sgr-like chemical abundances .
Of the 62 stars , 35 have Gaia kinematics and positions consistent with those predicted by N -body simulations of the Sgr stream , and are likely stars that have been stripped from Sgr during the last two pericenter passages ( < 2 Gyr ago ) .
Another 20 of the 62 stars exhibit chemical abundances indistinguishable from the Sgr stream stars , but are on highly eccentric orbits with median r _ { apo } \sim 25 kpc .
These stars are likely the ‘ ‘ accreted ’ ’ halo population thought to be the result of a separate merger with the MW 8-11 Gyr ago .
We also find one hypervelocity star candidate .
We conclude that Sgr was enriched to [ Fe/H ] \sim -0.2 before its most recent pericenter passage .
If the ‘ ‘ accreted halo ’ ’ population is from one major accretion event , then this progenitor galaxy was enriched to at least [ Fe/H ] \sim -0.6 , and had a similar star formation history to Sgr before merging .