Astrophys. J., 762, 28 (2013/January-1)
The most metal-poor stars. IV. The two populations with [Fe/H] ≲ -3.0.
NORRIS J.E., YONG D., BESSELL M.S., CHRISTLIEB N., ASPLUND M., GILMORE G., WYSE R.F.G., BEERS T.C., BARKLEM P.S., FREBEL A. and RYAN S.G.
Abstract (from CDS):
We discuss the carbon-normal and carbon-rich populations of Galactic halo stars having [Fe/H] ≲ -3.0, utilizing chemical abundances from high-resolution, high signal-to-noise model-atmosphere analyses. The C-rich population represents ∼28% of stars below [Fe/H] = -3.1, with the present C-rich sample comprising 16 CEMP-no stars, and two others with [Fe/H] ∼ -5.5 and uncertain classification. The population is O-rich ([O/Fe] ≳ +1.5); the light elements Na, Mg, and Al are enhanced relative to Fe in half the sample; and for Z > 20 (Ca) there is little evidence for enhancements relative to solar values. These results are best explained in terms of the admixing and processing of material from H-burning and He-burning regions as achieved by nucleosynthesis in zero-heavy-element models in the literature of "mixing and fallback" supernovae (SNe); of rotating, massive, and intermediate-mass stars; and of Type II SNe with relativistic jets. The available (limited) radial velocities offer little support for the C-rich stars with [Fe/H] < -3.1 being binary. More data are required before one could conclude that binarity is key to an understanding of this population. We suggest that the C-rich and C-normal populations result from two different gas cooling channels in the very early universe of material that formed the progenitors of the two populations. The first was cooling by fine-structure line transitions of C II and O I (to form the C-rich population); the second, while not well defined (perhaps dust-induced cooling?), led to the C-normal group. In this scenario, the C-rich population contains the oldest stars currently observed.
early universe - Galaxy: formation - Galaxy: halo - nuclear reactions, nucleosynthesis, abundances - stars: abundances
View the reference in ADS
To bookmark this query, right click on this link: simbad:2013ApJ...762...28N and select 'bookmark this link' or equivalent in the popup menu