  Carbon enhanced metal poor (CEMP) stars are a particular class of low
metalicity halo stars whose chemical analysis may provide important constrains
to the chemistry evolution of the Galaxy and to the models of mass transfer and
evolution of components in binary systems. Here, we present a detailed analysis
of the CEMP star CD-50$^\circ$776, using high resolution optical spectroscopy.
We found that CD-50$^\circ$776 has a metalicity [Fe/H]=-2.31 and a carbon
abundance [C/Fe]=+1.21. Analyzing the s-process elements and the europium
abundances, we show that this star is actually a CEMP-s star, based on the
criteria set in the literature to classify these chemically peculiar objects.
We also show that CD-50$^\circ$776 is a lead star, since it has a ratio
[Pb/Ce]=+0.97. In addition, we show that CD-50$^\circ$776 develops radial
velocity variations that may be attributed to the orbital motion in a binary
system. The abundance pattern of CD-50$^\circ$776 is discussed and compared to
other CEMP-s stars already reported in the literature to show that this star is
a quite exceptional object among the CEMP stars, particularly due to its low
nitrogen abundance. Explaining this pattern may require to improve the
nucleosynthesis models, and the evolutionary models of mass transfer and binary
interaction.
