Abstract:
The origin of enhanced abundance of heavy elements observed in the surface chemical composition of carbonenhanced metal-poor (CEMP) stars still remains poorly understood. Here, we present detailed abundance analysis
of seven CEMP stars based on high-resolution (R ∼ 50,000) spectra that reveal enough evidence of asymptotic
giant branch (AGB) stars being possible progenitors for these objects. For the objects HE 0110−0406, HE 1425
−2052, and HE 1428−1950, we present for the first time a detailed abundance analysis. Our sample is found to
consist of one metal-poor ([Fe/H] < −1.0) and six very metal-poor ([Fe/H] < −2.0) stars with enhanced carbon
and neutron-capture elements. We have critically analyzed the observed abundance ratios of [O/Fe], [Sr/Ba], and
[hs/ls] and examined the possibility of AGB stars being possible progenitors. The abundance of oxygen estimated
in the program stars is characteristic of AGB progenitors except for HE 1429−0551 and HE 1447+0102. The
estimated values of [Sr/Ba] and [hs/ls] ratios also support AGB stars as possible progenitors. The locations of the
program stars in the absolute carbon abundance A(C) versus [Fe/H] diagram, along with the Group I objects, hint
at the binary nature of the object. We have studied the chemical enrichment histories of the program stars based on
abundance ratios [Mg/C], [Sc/Mn], and [C/Cr]. Using [C/N] and 12C/13C ratios, we have examined whether any
internal mixing had modified their surface chemical compositions. Kinematic analysis shows that the objects HE
0110−0406 and HE 1447+0102 are thick-disk objects and the remaining five objects belong to the halo population
of the Galaxy.
