paper

Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of CEMP-no Stars

arXiv:1607.06336 · doi:10.3847/0004-637X/833/1/20

Abstract

We investigate anew the distribution of absolute carbon abundance, (C) (C), for carbon-enhanced metal-poor (CEMP) stars in the halo of the Milky Way, based on high-resolution spectroscopic data for a total sample of 305 CEMP stars. The sample includes 147 CEMP- (and CEMP-r/s) stars, 127 CEMP-no stars, and 31 CEMP stars that are unclassified, based on the currently employed [Ba/Fe] criterion. We confirm previous claims that the distribution of (C) for CEMP stars is (at least) bimodal, with newly determined peaks centered on (C) (the high-C region) and (C) (the low-C region). A very high fraction of CEMP- (and CEMP-r/s) stars belong to the high-C region, while the great majority of CEMP-no stars reside in the low-C region. However, there exists complexity in the morphology of the (C)-[Fe/H] space for the CEMP-no stars, a first indication that more than one class of first-generation stellar progenitors may be required to account for their observed abundances. The two groups of CEMP-no stars we identify exhibit clearly different locations in the (Na)-(C) and (Mg)-(C) spaces, also suggesting multiple progenitors. The clear distinction in (C) between the CEMP- (and CEMP-) stars and the CEMP-no stars appears to be , and , for the separation of these sub-classes as the previously recommended criterion based on [Ba/Fe] (and [Ba/Eu]) abundance ratios. This result opens the window for its application to present and future large-scale low- and medium-resolution spectroscopic surveys.

arXiv comment26pages, 7 figures, and 3 Tables ; Accepted for publication in ApJ; added more data and corrected minor inconsistencies existed in the compiled data of the previous studies

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