Abstract:
We have conducted detailed high-resolution spectroscopic studies on three extremely metal-poor (EMP) stars HE 0401−0138, HE 1153−0518, and HE 1246−1344. For the stars HE 0401−0138 and HE 1246−1344, we have estimated the abundances of C, Na, Mg, Ca, Sc, Ti, Cr, Mn, Co, Ni, Sr, and Ba along with the upper limits for Li, O, La, Ce, Pr, Nd, Sm, and Eu. For HE 1153−0518, abundances of seven light elements from C through Ni and two heavy elements, Y and Ba, have been derived, together with upper limits for Li, O, and La. Based on their observed abundance patterns, HE 0401−0138 and HE 1246−1344 are classified as normal EMP stars, whereas HE 1153−0518 is identified as a newly discovered CEMP-no star. HE 1153−0518 shows strong carbon enhancement with a high absolute carbon abundance, extreme sodium enrichment, very low neutron-capture element abundances, and a very low carbon isotopic ratio (12C/13C = 2.0). Its spectral energy distribution shows clear infrared excess, indicating the presence of circumstellar dust. The abundance pattern of HE 1153−0518 suggests enrichment by early nucleosynthetic processes, such as faint core-collapse supernovae with mixing and fallback, while the possibility of binary interaction and subsequent internal mixing cannot
be ruled out. The discovery and detailed study of HE 1153−0518 add an important object to the small population of highA(C) CEMP-no stars and provide valuable constraints on early chemical enrichment pathways and the nature of the first generations of stars.
