Chemical Abundances of new member stars in the Tucana II dwarf galaxy
  We present chemical abundance measurements for seven stars with metallicities
ranging from [Fe/H] = $-$3.3 to [Fe/H] = $-$2.4 in the Tucana II ultra-faint
dwarf galaxy (UFD), based on high-resolution spectra obtained with the MIKE
spectrograph on the 6.5 m Magellan-Clay Telescope. For three stars, we present
detailed chemical abundances for the first time. Of those, two stars are newly
discovered members of Tucana II and were selected as probable members from deep
narrow band photometry of the Tucana II UFD taken with the SkyMapper telescope.
This result demonstrates the potential for photometrically identifying members
of dwarf galaxy systems based on chemical composition. One new star was
selected from the membership catalog of Walker et al. (2016). The other four
stars in our sample have been re-analyzed, following additional observations.
Overall, six stars have chemical abundances that are characteristic of the UFD
stellar population. The seventh star shows chemical abundances that are
discrepant from the other Tucana II members and an atypical, higher strontium
abundance than what is expected for typical UFD stars. While unlikely, its
strontium abundance raises the possibility that it may be a foreground
metal-poor halo star with the same systemic velocity as Tucana II. If we were
to exclude this star, Tucana II would satisfy the criteria to be a surviving
first galaxy. Otherwise, this star implies that Tucana II has likely
experienced somewhat extended chemical evolution.
