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We present a high-resolution (R~35,000), high signal-to-noise (S/N>200)Magellan/MIKE spectrum of the star RAVE J094921.8-161722, a bright (V=11.3)metal-poor red giant star with [Fe/H] = -2.2, identified as a carbon-enhancedmetal-poor (CEMP) star from the RAVE survey. We report its detailed chemicalabundance signature of light fusion elements and heavy neutron-captureelements. We find J0949-1617 to be a CEMP star with s-process enhancement thatmust have formed from gas enriched by a prior r-process event. Lightneutron-capture elements follow a low-metallicity s-process pattern, while theheavier neutron-capture elements above Eu follow an r-process pattern. The Pbabundance is high, in line with an s-process origin. Thorium is also detected,as expected from an r-process origin, as Th is not produced in the s-process.We employ nucleosynthesis model predictions that take an initial r-processenhancement into account, and then determine the mass transfer of carbon ands-process material from a putative more massive companion onto the observedstar. The resulting abundances agree well with the observed pattern. Weconclude that J0949-1617 is the first bonafide CEMP-r+s star identified. Thisclass of objects has previously been suggested to explain stars withneutron-capture element patterns that originate from neither the r- ors-process alone. We speculate that J0949-1617 formed in an environment similarto those of ultra-faint dwarf galaxies like Tucana III and Reticulum II, whichwere enriched in r-process elements by one or multiple neutron star mergers atthe earliest times.a

The R-Process Alliance: Discovery of the first metal-poor star with a combined r- and s-process element signature