Chemical abundances in the leiptr stellar stream: a disrupted ultra-faint dwarf galaxy?

Chemical abundances of stellar streams can be used to determine the nature of a stream’s progenitor. Here we study the progenitor of the recently discovered Leiptr stellar stream, which was previously suggested to be a tidally disrupted halo globular cluster. We obtain high-resolution spectra of five red giant branch stars selected from the Gaia DR2 STREAMFINDER catalog with Magellan/MIKE. One star is a clear non-member. The remaining four stars display chemical abundances consistent with those of a low-mass dwarf galaxy: they have a low mean metallicity, ⟨[Fe/H]⟩ = −2.2; they do not all have identical metallicities; and they display low [α/Fe] ∼ 0 and [Sr/Fe] and [Ba/Fe] ∼ −1. This pattern of low α and neutron-capture element abundances is only found in intact dwarf galaxies with stellar mass ≲ 10⁵ M_⊙. Although more data are needed to be certain, Leiptr’s chemistry is consistent with being the lowest-mass dwarf galaxy stream without a known intact progenitor, possibly in the mass range of ultra-faint dwarf galaxies. Leiptr thus preserves a record of one of the lowest-mass early accretion events into the Milky Way.