The Pristine survey -- XII: Gemini-GRACES chemo-dynamical study of newly
  discovered extremely metal-poor stars in the Galaxy
  High-resolution optical spectra of 30 metal-poor stars selected from the
\Pristine\ survey are presented, based on observations taken with the Gemini
Observatory GRACES spectrograph. Stellar parameters \teff and \logg are
determined using a Gaia DR2 colour-temperature calibration and surface gravity
from the Stefan-Boltzmann equation. GRACES spectra are used to determine
chemical abundances (or upper-limits) for 20 elements (Li, O, Na, Mg, K, Ca,
Ti, Sc, Cr, Mn, Fe, Ni, Cu, Zn, Y, Zr, Ba, La, Nd, Eu). These stars are
confirmed to be metal-poor ([Fe/H]$<-2.5$), with higher precision than from
earlier medium-resolution analyses. The chemistry for most targets is similar
to other extremely metal-poor stars in the Galactic halo. Three stars near
[Fe/H]$=-3.0$ have unusually low Ca and high Mg, suggestive of contributions
from few SN~II where alpha-element formation through hydrostatic
nucleosynthesis was more efficient. Three new carbon-enhanced metal-poor stars
are also identified (two CEMP-s and one potential CEMP-no star) when our
chemical abundances are combined with carbon from previous medium-resolution
analyses. The GRACES spectra also provide precision radial velocities
($\sigma_{\rm RV}\le0.2$km\,s$^{-1}$) for dynamical orbit calculations with the
Gaia DR2 proper motions. Most of our targets are dynamically associated with
the Galactic halo; however, five stars with [Fe/H]$<-3$ have planar-like
orbits, including one retrograde star. Another five stars are dynamically
consistent with the Gaia-Sequoia accretion event; three have typical halo
[$\alpha$/Fe] ratios for their metallicities, whereas two are
[Mg/Fe]-deficient, and one is a new CEMP-s candidate. These results are
discussed in terms of the formation and early chemical evolution of the Galaxy.
