Chemodynamical study of two CEMP-no stars from the Hamburg/ESO Survey

Abstract

The Carbon-Enhanced Metal-Poor (CEMP) stars with no enhancement of neutron-capture elements, the so-called CEMP-no stars are believed to be the direct descendants of first-generation stars and provide a unique opportunity to probe the early Galactic nucleosynthesis. We present a detailed chemical and kinematic analysis for two extremely metal-poor stars HE 1243 − 2408 and HE 0038 − 0345 using high-resolution (R∼86 000) HERMES spectra. For the object HE 1243 − 2408, we could make a detailed comparison with the available literature values; however, only limited information is available for the other object HE 0038 − 0345. Our estimated metallicity for these two objects are −3.05 and −2.92, respectively. With estimated [C/Fe] (1.03 and 1.05) and [Ba/Fe] (−0.18 and −0.11), respectively, the objects are found to be bonafide CEMP-no stars. From the observed abundances of C, Na, Mg, and Ba (i.e. A(C), A(Na), A(Mg), A(Ba)), the objects are found to belong to Group II CEMP-no stars. A detailed abundance profile analysis indicates that the objects are accreted from dSph satellite galaxies that support hierarchical galaxy assembly. Further, our analysis shows that the progenitors of the stars are likely Pop II Core-Collapse Supernovae. The object HE 0038 − 0345 is found to be a high-energy, prograde, outer-halo object, and HE 1243 − 2408 is found to be a high-energy, retrograde, inner-halo object. Our detailed chemodynamical analysis shows that HE 1243 − 2408 is related to I’itoi structure, where as HE 0038 − 0345 is likely related to Sgr or GSE events. The mass of the progenitor galaxies of the programme stars inferred from their dynamics is at par with their likely origin in massive dSph galaxies.