We present an abundance analysis of six member stars of the recently discovered Aquarius stream , in an attempt to ascertain whether this halo stream is real and , if so , to understand its origin .
The mean metallicities of the six stars have a dispersion of only 0.10 dex , indicating that they are part of a chemically coherent structure .
We then investigate whether the stream represents the debris of a disrupted dwarf galaxy or a disrupted globular cluster .
The [ Ni/Fe ] - [ Na/Fe ] plane provides a good diagnostic : globular cluster stars and dwarf spheroidal galaxy stars are well separated in this plane , and the Aquarius stream stars lie unambiguously in the globular cluster region .
The Aquarius stream stars also lie on the distinct [ Na/Fe ] - [ O/Fe ] and [ Mg/Fe ] - [ Al/Fe ] relations delineated by Galactic globular cluster stars .
Spectroscopic parameters for the six Aquarius stars show that they are tightly confined to a 12 Gyr , [ Fe/H ] = -1.0 , alpha-enhanced isochrone , consistent with their identification as globular cluster debris .
We present evidence that the Aquarius stream may continue through the disk and out into the northern halo .
Our results indicate a globular cluster origin for the Aquarius stream , and demonstrate the potential for chemical tagging to identify the origins of Galactic substructures .