Oxygen abundances of carbon-enhanced stellar population in the halo.

The large fraction of carbon-enhanced metal-poor (CEMP) stars at lower metallicities makes them an interesting class of objects to be probed further in greater detail. They show different abundance patterns of neutron-capture elements and based on that CEMP stars are further divided into four categories. Abundances of C, N and O, along with other elements, are required to understand the different nucleosynthetic origins of the subclasses and their progenitors. We studied nine bright carbon-enhanced stars from the Milky Way halo in a metallicity range from −0.8 to −2.5. They show enhancement in C, N, O and Ba and exhibit radial velocity variation. This indicates the presence of a binary companion which might have contributed to the enhanced carbon and s-process abundance through mass transfer during its asymptotic-giant-branch (AGB) phase of evolution. Their abundance pattern of C, N and O favors low-mass nature for their binary companion. [ABSTRACT FROM AUTHOR]