  We performed a detailed, high-resolution spectroscopic analysis of HE
1005-1439 based on SUBARU/HDS spectra with an R ~ 50000. Abundances of ten
light elements from C through Ni and twelve heavy elements Sr, Y, Ba, La, Ce,
Pr, Nd, Eu, Dy, Er, Hf, and Pb were determined. We also performed a
parametric-model-based analysis of the abundances of the heavy elements to
understand the origin of the observed abundance pattern. For the first time, we
came across an object with a surface chemical composition that exhibits
contributions from both slow (s) and intermediate (i) neutron-capture
nucleosynthesis. The observed abundance pattern is unique and has never been
observed in any CEMP stars. The star is found to be a CEMP-s star based on the
CEMP stars' classification criteria. However, the observed abundance pattern
could not be explained based on theoretical s-process model predictions. On the
contrary, our parametric-model based analysis clearly indicates its surface
chemical composition being influenced by similar contributions from both the s-
and i-process. We critically examined the observed abundances and carefully
investigated the formation scenarios involving s-process and i-process that are
available in literature, and we found that none of them could explain the
observed abundances. We note that the variation we see in our radial velocity
estimates obtained from several epochs may indicate the presence of a binary
companion. Considering a binary system, we, therefore, propose a formation
scenario for this object involving effective proton ingestion episodes (PIEs)
triggering i-process nucleosynthesis followed by s-process asymptotic giant
branch (AGB) nucleosynthesis with a few third-dredge-up (TDU) episodes in the
now extinct companion AGB star. Results obtained from the
parametric-model-based analysis are discussed in light of existing stellar
evolutionary models.
