The lowest detected stellar Fe abundance: the halo star SMSS J160540.18-144323.1
Schmidt, B. P.; Da Costa, G. S.; Marino, A. F.; Yong, D.; Asplund, M.; Mackey, A. D.; Lind, K.; Nordlander, T.; Bessell, M. S.; Norris, J. E.; Frebel, A.; Chiti, A.; Murphy, S. J.; Casey, A. R.; Ezzeddine, R.
Australia, United States, Germany, Sweden, Italy
Abstract
We report the discovery of SMSS J160540.18-144323.1, a new ultra metal-poor halo star discovered with the SkyMapper telescope. We measure [{Fe}/{H}]= -6.2 ± 0.2 (1D LTE), the lowest ever detected abundance of iron in a star. The star is strongly carbon-enhanced, [{C}/{Fe}] = 3.9 ± 0.2, while other abundances are compatible with an α-enhanced solar-like pattern with [{Ca}/{Fe}] = 0.4 ± 0.2, [{Mg}/{Fe}] = 0.6 ± 0.2, [{Ti}/{Fe}] = 0.8 ± 0.2, and no significant s- or r-process enrichment, [{Sr}/{Fe}] < 0.2 and [{Ba}/{Fe}] < 1.0 (3σ limits). Population III stars exploding as fallback supernovae may explain both the strong carbon enhancement and the apparent lack of enhancement of odd-Z and neutron-capture element abundances. Grids of supernova models computed for metal-free progenitor stars yield good matches for stars of about 10 M_⊙ imparting a low kinetic energy on the supernova ejecta, while models for stars more massive than roughly 20 M_⊙ are incompatible with the observed abundance pattern.