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A radial-velocity monitoring of the Carbon-Enhanced Metal-Poor (CEMP) star HE0017+0055 over 8 years with the Nordic Optical Telescope and Mercatortelescopes reveals variability with a period of 384 d and amplitude of540$\pm27$ m s$^{-1}$, superimposed on a nearly linear long-term decline of$\sim$1 m s$^{-1}$ day$^{-1}$. High-resolution HERMES/Mercator and Keck/HIRESspectra have been used to derive elemental abundances using 1-D LTE MARCSmodels. A metallicity of [Fe/H] $\sim -2.4$ is found, along with s-processoverabundances on the order of 2 dex (with the exception of [Y/Fe] $\sim+0.5$),and most notably overabundances of r-process elements like Sm, Eu, Dy, and Erin the range 0.9 - 2.0 dex. With [Ba/Fe] $ > 1.9$ dex and [Eu/Fe] = 2.3 dex, HE0017+0055 is a CEMP-rs star. It appears to be a giant star below the tip of thered giant branch (RGB). The s-process pollution must therefore originate frommass transfer from a companion formerly on the AGB, now a carbon-oxygen whitedwarf (WD). If the 384 d velocity variations are attributed to the WDcompanion, its orbit must be seen almost face-on, with $i \sim 2.3^\circ$,because the mass function is very small: $f(M_1,M_2) =(6.1\pm1.1)\times10^{-6}$ Msun. Alternatively, the WD orbital motion could beresponsible for the long-term velocity variations, with a period of severaldecades. The 384 d variations should then be attributed either to a low-massinner companion (perhaps a brown dwarf, depending on the orbital inclination),or to stellar pulsations. The latter possibility is made likely by the factthat similar low-amplitude velocity variations, with periods close to 1 yr,have been reported for other CEMP stars in a companion paper (Jorissen et al.,2015). A definite conclusion about the origin of the 384 d velocity variationsshould however await the detection of synchronous low-amplitude photometricvariations.

HE 0017+0055 : A probable pulsating CEMP-rs star and long-period binary