Chemical analysis of two extremely metal-poor stars HE 2148-2039 and HE 2155-2043

Abstract

We present elemental abundance results for HE 2148-2039 and HE 2155-2043 based on a detailed high-resolution spectroscopic analysis. The high-resolution SUBARU/HDS spectra used for our analysis have a resolution of R~60 000. Although limited information based on photometry and low-resolution spectroscopy are available, we present for the first time an abundance analysis based on high-resolution spectra for both the objects. Our analysis shows that the two objects are extremely metal-poor with [Fe/H]< -3. Among the neutron-capture elements, abundances of only Sr and Ba could be determined in our programme stars. For both the objects [Ba/Fe] is found to be < 0. While strontium is under abundant in HE 2148-2039 with [Sr/Fe]~ -2.02, Sr is near solar in HE 2155-2043. The locations of the programme stars in the absolute carbon abundance, A(C) vs. [Fe/H] diagram show that HE 2148-2039 is a CEMP-no Group II object and HE 2155-2043 is a CEMP-no Group III object. Observed [Sr/Ba] ratios are characteristics of a fast rotating massive star progenitor for HE 2155-2043 and a metal-poor Asymptotic giant branch (AGB) star for HE 2148-2039. The estimated [Sc/Mn] as well as [C/Cr] ratios in HE 2155-2043 show that the surface chemical composition of this object is mono-enriched. The surface chemical composition of HE 2148-2039 is also found to be mono-enriched based on [Mg/C] ratio. With respect to their locations in the [C/N] vs. T eff diagram, HE 2148-2039 shows signatures of mixing, and HE 2155-2043 falls in the unmixed region of [C/N] vs. Teff plot. Kinematic analysis shows that both the objects belong to Galactic halo population.

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