Sagittarius ( Sgr ) is a massive disrupted dwarf spheroidal galaxy in the Milky Way halo that has undergone several stripping events .
Previous chemical studies were restricted mainly to a few , metal-rich ( [ Fe/H ] \gtrapprox - 1 ) stars that suggested a top-light initial mass function ( IMF ) .
Here we present the first high-resolution , very metal-poor ( [ Fe/H ] = -1 to -3 ) sample of 13 giant stars in the main body of Sgr .
We derive abundances of 13 elements namely C , Ca , Co , Fe , Sr , Ba , La , Ce , Nd , Eu , Dy , Pb , and Th which challenge the interpretation based on previous studies .
Our abundances from Sgr mimic those of the metal-poor halo and our most metal-poor star ( [ Fe/H ] \sim - 3 ) indicates a pure r-process pollution .
Abundances of Sr , Pb , and Th are presented for the first time in Sgr , allowing for age determination using nuclear cosmochronology .
We calculate ages of 9 \pm 2.5 Gyr .
Most of the sample stars have been enriched by a range of asymptotic giant branch ( AGB ) stars with masses between 1.3 and 5 M _ { \odot } .
Sgr J190651.47-320147.23 shows a large overabundance of Pb ( 2.05 dex ) and a peculiar abundance pattern best fit by a 3 M _ { \odot } AGB star .
Based on star-to-star scatter and observed abundance patterns a mixture of low- and high-mass AGB stars and supernovae ( 15-25 M _ { \odot } ) are necessary to explain these patterns .
The high level ( 0.29 \pm 0.05 dex ) of Ca indicates that massive supernovae must have existed and polluted the early ISM of Sgr before it lost its gas .
This result is in contrast with a top-light IMF with no massive stars polluting Sgr .