High Resolution Optical Spectroscopy of Stars in the Sylgr Stellar
  Stream
  We observe two metal-poor main sequence stars that are members of the
recently-discovered Sylgr stellar stream. We present radial velocities, stellar
parameters, and abundances for 13 elements derived from high-resolution optical
spectra collected using the Magellan Inamori Kyocera Echelle spectrograph. The
two stars have identical compositions (within 0.13 dex or 1.2 sigma) among all
elements detected. Both stars are very metal poor ([Fe/H] = -2.92 +/- 0.06).
Neither star is highly enhanced in C ([C/Fe] < +1.0). Both stars are enhanced
in the alpha elements Mg, Si, and Ca ([alpha/Fe] = +0.32 +/- 0.06), and ratios
among Na, Al, and all Fe-group elements are typical for other stars in the halo
and ultra-faint and dwarf spheroidal galaxies at this metallicity. Sr is mildly
enhanced ([Sr/Fe] = +0.22 +/- 0.11), but Ba is not enhanced ([Ba/Fe] < -0.4),
indicating that these stars do not contain high levels of neutron-capture
elements. The Li abundances match those found in metal-poor unevolved field
stars and globular clusters (log epsilon (Li) = 2.05 +/- 0.07), which implies
that environment is not a dominant factor in determining the Li content of
metal-poor stars. The chemical compositions of these two stars cannot
distinguish whether the progenitor of the Sylgr stream was a dwarf galaxy or a
globular cluster. If the progenitor was a dwarf galaxy, the stream may
originate from a dense region such as a nuclear star cluster. If the progenitor
was a globular cluster, it would be the most metal-poor globular cluster known.
