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We performed a detailed, high-resolution spectroscopic analysis of HE1005-1439 based on SUBARU/HDS spectra with an R ~ 50000. Abundances of tenlight 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 aparametric-model-based analysis of the abundances of the heavy elements tounderstand the origin of the observed abundance pattern. For the first time, wecame across an object with a surface chemical composition that exhibitscontributions from both slow (s) and intermediate (i) neutron-capturenucleosynthesis. The observed abundance pattern is unique and has never beenobserved in any CEMP stars. The star is found to be a CEMP-s star based on theCEMP stars' classification criteria. However, the observed abundance patterncould not be explained based on theoretical s-process model predictions. On thecontrary, our parametric-model based analysis clearly indicates its surfacechemical composition being influenced by similar contributions from both the s-and i-process. We critically examined the observed abundances and carefullyinvestigated the formation scenarios involving s-process and i-process that areavailable in literature, and we found that none of them could explain theobserved abundances. We note that the variation we see in our radial velocityestimates obtained from several epochs may indicate the presence of a binarycompanion. Considering a binary system, we, therefore, propose a formationscenario for this object involving effective proton ingestion episodes (PIEs)triggering i-process nucleosynthesis followed by s-process asymptotic giantbranch (AGB) nucleosynthesis with a few third-dredge-up (TDU) episodes in thenow extinct companion AGB star. Results obtained from theparametric-model-based analysis are discussed in light of existing stellarevolutionary models.

astronomy and astrophysics

The peculiar abundances of HE 1005-1439. A carbon-enhanced extremely  metal-poor star contaminated with products of both s-and i-process  nucleosynthesis