Chemo-Dynamically Tagged Groups of CEMP Stars in the Halo of the Milky Way. I. Untangling the Origins of CEMP-$s$ and CEMP-no Stars

Abstract

We construct a sample of 644 carbon-enhanced metal-poor (CEMP) stars with abundance analyses based on moderate- to high-resolution spectroscopic studies. Dynamical parameters for these stars are estimated, based on radial velocities, Bayesian parallax-based distance estimates, and proper motions from $Gaia$ EDR3 and DR3, supplemented by additional available information where needed. After separating our sample into the different CEMP morphological groups in the Yoon-Beers Diagram of absolute carbon abundance vs. metallicity, we used the derived specific energies and actions (E, J${}_r$, J${}_{\varphi }$, J${}_z$) to cluster them into Chemo-Dynamically Tagged Groups (CDTGs). We then analyzed the elemental-abundance dispersions within these clusters by comparing them to the dispersion of clusters that were generated at random. We find that, for the Group I (primarily CEMP-$s$ and CEMP-$r/s$) clustered stars, there exist statistically insignificant intra-cluster dispersions in [Fe/H], $[\text{C}/\text{Fe}{]}_c$ (evolution corrected carbon), and [Mg/Fe] when compared to the intra-cluster dispersions of randomly clustered Group I CEMP stars. In contrast, the Group II (primarily CEMP-no) stars exhibit clear similarities in their intra-cluster abundances, with very low, statistically significant, dispersions in $[\text{C}/\text{Fe}{]}_c$. and marginally significant results in [Mg/Fe]. These results strongly indicate that Group I CEMP stars received their carbon enhancements from local phenomena, such as mass transfer from a evolved binary companion in regions with extended star-formation histories, while the CDTGs of Group II CEMP stars formed in low-metallicity environments that had already been enriched in carbon, likely from massive rapidly rotating ultra and hyper metal-poor stars and/or supernovae associated with high-mass early generation stars.

Accepted to APJ Journals. arXiv admin note: substantial text overlap with arXiv:2208.09712

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