Astrophys. J., 879, 37-37 (2019/July-1)
The most metal-poor stars. V. The CEMP-no stars in 3D and non-LTE.
NORRIS J.E. and YONG D.
Abstract (from CDS):
We explore the nature of carbon-rich ([C/Fe]1D,LTE > +0.7), metal-poor ([Fe/H1D,LTE] < -2.0) stars in the light of post 1D,LTE literature analyses, which provide 3D-1D and NLTE-LTE corrections for iron, and 3D-1D corrections for carbon (from the CH G-band, the only indicator at lowest [Fe/H]). High-excitation C I lines are used to constrain 3D,NLTE corrections of G-band analyses. Corrections to the 1D,LTE compilations of Yoon et al. and Yong et al. yield 3D,LTE and 3D,NLTE Fe and C abundances. The number of CEMP-no stars in the Yoon et al. compilation (plus eight others) decreases from 130 (1D,LTE) to 68 (3D,LTE) and 35 (3D,NLTE). For stars with -4.5 < [Fe/H] < -3.0 in the compilation of Yong et al., the corresponding CEMP-no fractions change from 0.30 to 0.15 and 0.12, respectively. We present a toy model of the coalescence of pre-stellar clouds of the two populations that followed chemical enrichment by the first zero-heavy-element stars: the C-rich, hyper-metal-poor and the C-normal, very-metal-poor populations. The model provides a reasonable first-order explanation of the distribution of the 1D,LTE abundances of CEMP-no stars in the A(C) and [C/Fe] versus [Fe/H] planes, in the range -4.0 < [Fe/H] < -2.0. The Yoon et al. CEMP Group I contains a subset of 19 CEMP-no stars (14% of the group), four out of nine of which are binary, and which have large [Sr/Ba]1D,LTE values. The data support the conjectures of Hansen et al. and Arentsen et al. that these stars may have experienced enrichment from asymptotic giant branch stars and/or "spinstars."
© 2019. The American Astronomical Society. All rights reserved.
early universe - Galaxy: formation - Galaxy: halo - nuclear reactions, nucleosynthesis, abundances - stars: abundances
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