  Aims. The Chemical Evolution of R-process Elements in Stars (CERES) project
aims to provide a homogeneous analysis of a sample of metal-poor stars
([Fe/H]<-1.5). We present the stellar parameters and the chemical abundances of
elements up to Zr for a sample of 52 giant stars.Methods. We relied on a sample
of high signal-to-noise UVES spectra. We determined stellar parameters from
Gaia photometry and parallaxes. Chemical abundances were derived using spectrum
synthesis and model atmospheres.Results. We determined chemical abundances of
26 species of 18 elements: Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni,
Cu, Zn, Sr, Y, and Zr. For several stars, we were able to measure both neutral
and ionised species, including Si, Sc, Mn, and Zr. We have roughly doubled the
number of measurements of Cu for stars at [Fe/H] <= -2.5. The homogeneity of
the sample made it possible to highlight the presence of two Zn-rich stars
([Zn/Fe]~+0.7), one r-rich and the other r-poor. We report the existence of two
branches in the [Zn/Fe] versus [Ni/Fe] plane and suggest that the high [Zn/Fe]
branch is the result of hypernova nucleosynthesis. We discovered two stars with
peculiar light neutron-capture abundance patterns: CES1237+1922 (also known as
BS 16085-0050), which is ~1 dex underabundant in Sr, Y, and Zr with respect to
the other stars in the sample, and CES2250-4057 (also known as HE 2247-4113),
which shows a ~1 dex overabundance of Sr with respect to Y and Zr.Conclusions.
The high quality of our dataset allowed us to measure hardly detectable ions.
This can provide guidance in the development of line formation computations
that take deviations from local thermodynamic equilibrium and hydrodynamical
effects into account.
